I was standing in line at a coffee shop in Chicago last month, expecting an urgent call from my real estate agent regarding an offer on a house. While listening to a colleague ramble on a routine work call, my Galaxy S-Series device stayed dead silent. No double-beep in my ear. No floating pop-up screen. Nothing. It was only when I hung up that a voicemail notification popped up: my agent had tried calling, assumed I was ignoring him, and moved on. My phone had quietly dropped his incoming call straight to voicemail without giving me a chance to put my first call on hold. When I opened my Phone app to check my settings, the Call Waiting toggle under Supplementary Services was spinning endlessly before throwing a cryptic error: "Failed to read data. Network or SIM card error."
If you are experiencing this exact issue on your Samsung Galaxy device in the United States, you are not alone. Whether you are running an unlocked Snapdragon flagship or a carrier-locked model, Call Waiting glitches are frustratingly common across major US networks. This comprehensive guide breaks down why this feature fails on Samsung devices and provides step-by-step solutions to restore second-call notifications immediately.
Quick Answer
To fix the Samsung Call Waiting glitch, open your Phone app, tap the three dots in the upper right corner, navigate to Settings > Supplementary Services, and ensure Call Waiting is toggled on. If the option is greyed out or displays a reading error, open your phone dialer and force-enable the feature using the universal US carrier MMI star code *43#. If the error persists, temporarily disable any active Private DNS settings (such as AdGuard), turn off Wi-Fi Calling, and clear the data for the system app named com.samsung.android.incallui.
Why This Matters
Call Waiting is not just a luxury; it is a fundamental pillar of modern mobile communication. In a fast-paced work and personal environment, missing a second incoming call can lead to significant real-world consequences:
- Professional Reliability: Important business clients, job interviewers, or medical providers are sent straight to voicemail, making you appear unavailable or unresponsive.
- Urgent Family Communications: Emergency calls from family members or schools fail to interrupt non-essential conversations, leaving you unaware of urgent situations.
- Carrier Provisioning Verification: A failing Supplementary Services menu often indicates underlying IMS (IP Multimedia Subsystem) or VoLTE registration desynchronization between your Galaxy device and your carrier's cell towers.
- Device Efficiency: Background crashes in Samsung's in-call display components (
com.samsung.android.incallui) can cause unexpected battery drain and dialer lag during active voice calls.
Understanding the Root Causes on US Carrier Networks
The Call Waiting glitch on Samsung Galaxy devices rarely stems from broken hardware. Instead, it is typically caused by software configuration mismatches between Samsung's One UI software and US cellular network infrastructure. According to user reports on the official Samsung US support documentation, several distinct factors cause this feature to fail:
1. Carrier Supplementary Services API Lockouts
In One UI 7.x and One UI 8.x, Samsung changed how the stock Phone app communicates with cellular networks. Rather than relying solely on local device settings, opening the Supplementary Services menu forces your device to send a real-time query to your carrier's Home Location Register (HLR). On major US networks like Verizon, AT&T, and T-Mobile, this query often times out due to strict security policies, displaying the infamous "Failed to read data" pop-up.
2. Private DNS and AdBlocker Conflicts
Many US Samsung users configure custom Private DNS profiles (such as dns.adguard.com or NextDNS) to block system-wide mobile ads. However, these DNS providers frequently block the background domain lookup requests that Samsung's telephony service uses to verify your account's feature status with the carrier, causing the Call Waiting toggle to freeze or fail.
3. Wi-Fi Calling Handover Errors
When Wi-Fi Calling is enabled and set to "Wi-Fi Preferred," incoming call signaling is routed through an encrypted IPSec tunnel to your carrier. If your local Wi-Fi network experiences packet loss or strict firewall rules, your carrier's server may fail to transmit the second-call alert signal to your phone while you are actively using cellular voice bandwidth.
4. Unlocked (U1) Firmware CSC Mismatches
If you purchased an unlocked factory model (e.g., SM-S928U1 or SM-S938U1) and inserted a physical SIM or eSIM from a major US carrier, your device uses a universal Carrier Specific Customization (CSC) profile. Major system updates occasionally disrupt this CSC profile, causing the Phone app to lose its connection to network-level call settings.
Comprehensive Step-by-Step Fixes for Samsung Call Waiting
Follow these proven troubleshooting methods in order, starting with the fastest and least invasive solutions.
Fix 1: Force-Enable Call Waiting via US Carrier MMI Star Codes
When the graphical user interface inside One UI fails to update your settings, you can bypass the Phone app's visual menu entirely by communicating directly with your carrier's switchboard using native MMI (Man-Machine Interface) star codes.
- Open your stock Samsung Phone app.
- Tap the Keypad tab.
- Dial *43# and press the green Call button.
- Wait a few seconds for an MMI pop-up notification to appear on your screen.
- You should see a message stating: "Call Waiting service was enabled."
- To verify your current status at any time, dial *#43# and press Call.
| US Carrier | Enable Code | Disable Code | Check Status Code |
|---|---|---|---|
| T-Mobile / Metro by T-Mobile | *43# | #43# | *#43# |
| AT&T / Cricket Wireless | *43# | #43# | *#43# |
| Verizon / Visible | *43# (or via My Verizon App) | #43# | *#43# |
Verification Check: Call your Galaxy phone from a secondary landline or friend's phone while you are actively on another call. If you hear a faint double-beep in your ear and see the incoming call overlay screen, the MMI force command succeeded.
Fix 2: Disable Custom Private DNS & AdBlocker Configurations
Custom Private DNS settings are a leading cause of greyed-out Supplementary Services options on US Samsung devices.
- Open Settings on your Samsung Galaxy device.
- Tap Connections.
- Scroll down and select More connection settings.
- Tap Private DNS.
- Change the selection from Private DNS provider hostname to Off or Automatic.
- Tap Save.
- Force close your Phone app, reopen it, and navigate back to Phone App > 3 Dots > Settings > Supplementary Services to see if the menu loads properly.
Verification Check: Upon opening Supplementary Services, the loading wheel should resolve within 3-5 seconds, displaying accessible, togglable switches for both Call Waiting and Call Forwarding.
Fix 3: Adjust Wi-Fi Calling Handover Preferences
If your device is stuck deciding between Wi-Fi and cellular networks during an incoming call, second-call alerts can be lost during the handover phase.
- Open Settings and tap Connections.
- Tap Wi-Fi Calling (or tap the text label, not just the toggle switch).
- Select Calling preference.
- Change the mode to Cellular preferred (or Mobile network preferred).
- If your carrier (such as Verizon) locks this setting, turn off Wi-Fi Calling entirely while troubleshooting your second-call notifications.
Fix 4: Clear Data for Call Handling System Apps
Corrupt temporary cache files in Samsung's core telephony system apps can prevent call overlays from appearing over active full-screen applications.
- Open Settings and select Apps.
- Tap the Filter and sort icon (the small icon next to "Your apps") and toggle on Show system apps. Tap OK.
- Scroll down or use the search bar to find Phone (there may be multiple entries; apply these steps to all of them).
- Tap Storage, then tap Clear Cache and Clear Data.
- Go back to the system app list and search for com.samsung.android.incallui (or InCallUI).
- Tap Storage, then select Clear Cache and Clear Data.
- Restart your Samsung Galaxy phone.
Verification Check: Place a test call. When a second call comes in, your phone should properly display the full-screen green and red answer/reject sliders along with the "Hold current call & Answer" prompt.
Fix 5: Reset Mobile Network Settings
Resetting your network configurations clears corrupt carrier provisioning profiles, stale access point names (APNs), and misconfigured Bluetooth or Wi-Fi handshakes without erasing your personal data or photos.
- Open Settings and scroll down to select General management.
- Tap Reset.
- Select Reset mobile network settings (on older One UI versions, this may be listed as Reset network settings).
- Tap Reset settings and enter your lock screen PIN or pattern to confirm.
- Your device will re-establish its connection to your carrier's cell towers and automatically download fresh network configuration profiles.
If your Samsung device continues to experience persistent cellular signaling failures, greyed-out options, or missing carrier icons across major network updates, the underlying issue may be rooted deeper within your device's IMS registration framework. To resolve complex voice configuration issues on major US carriers, check out our detailed guide on How to Fix Samsung VoLTE Icon Missing or Disabled to ensure your device maintains seamless voice-over-LTE connectivity.
Fix 6: Check Carrier Account Provisioning and Spam Shield Apps
Sometimes the issue lies on your carrier's account management side or with third-party call filtering applications. According to technical analysis by Android Police technical reports, built-in carrier spam shields can mistakenly block second calls if they flag the incoming caller as potential spam.
- Verizon Call Filter / AT&T ActiveArmor / T-Mobile Scam Shield: Open your carrier's dedicated security app and check your block logs. Ensure that high-level screening is not automatically routing unknown second calls straight to voicemail.
- Carrier Account Provisioning: Log into your official carrier account app (e.g., My Verizon, My AT&T) and verify that the "Call Waiting" feature is listed as active under your plan's line features. If it is missing, contact carrier customer service to re-provision the feature on your account.
Pro Tip: Force-Refresh Carrier Provisioning Using the Hidden Samsung Phone Diagnostic Menu
If you suspect your unlocked Samsung Galaxy device is suffering from an incomplete CSC network handshake after a One UI update, you can trigger a deep-level network re-registration using Samsung's built-in diagnostic dialer code.
Open your stock Samsung Phone app dialer and enter *#*#4636#*#* (or *#2263# for band selection menus on select Snapdragon models). If accessible on your carrier firmware build, select Phone Information, tap the three dots in the upper right corner, and select Trigger Carrier Provisioning. This forces your Snapdragon modem to execute a full re-authorization cycle with your carrier's IMS servers, re-enabling greyed-out Supplementary Services toggles without requiring a full factory reset.
Troubleshooting Matrix: Solutions by One UI Version & Hardware
Use this reference matrix to quickly identify the fixes best suited for your device's software version and hardware platform.
| One UI Version / Device | Primary Symptom | Most Effective Solution |
|---|---|---|
| One UI 8.x / 7.x (Snapdragon Flagships) | Supplementary Services infinite loading screen or network error. | Turn off Private DNS; use MMI code *43#. |
| Unlocked US Models (U1 Series) | Call Waiting toggle greyed out after major software update. | Reset Mobile Network Settings; contact carrier for IMS re-provisioning. |
| Galaxy A-Series (Exynos Variants) | Calls drop to voicemail while connected to Wi-Fi Calling. | Change Wi-Fi Calling preference to Cellular Preferred. |
| Dual-SIM / eSIM Configurations | Call Waiting works on Line 1, but fails completely on Line 2. | Enable "Auto data switching" under SIM Manager settings. |
Samsung Call Waiting Checklist
Follow this checklist to systematically resolve your Call Waiting issues:
- ✓ Open Phone App > 3 Dots > Settings > Supplementary Services and check if Call Waiting is enabled.
- ✓ Force-enable the feature by dialing *43# on your keypad.
- ✓ Navigate to Connections > More Connection Settings and set Private DNS to Off.
- ✓ Set Wi-Fi Calling preferences to Cellular Preferred.
- ✓ Clear cache and data for system apps Phone and com.samsung.android.incallui.
- ✓ Perform a Reset Mobile Network Settings inside General Management.
- ✓ Verify that carrier spam apps (Verizon Call Filter, AT&T ActiveArmor, T-Mobile Scam Shield) are not auto-blocking incoming calls.
- ✓ Test second-call functionality by placing an incoming call while actively connected to a voice call.
Conclusion
A failing Call Waiting feature on your Samsung Galaxy phone can disrupt your workflow and cause you to miss important calls. Fortunately, you rarely need to send your device in for repair or perform a full factory reset to fix it. In almost every case, the glitch can be resolved by executing direct MMI codes like *43#, disabling third-party Private DNS services that block background network checks, or clearing corrupt data in Samsung's call interface system apps.
By following the steps in this guide, you can restore proper second-call pop-ups and audio alerts on your Samsung device regardless of your carrier. If you found this troubleshooting guide helpful, share it with fellow Samsung Galaxy users or leave a comment below letting us know which step worked for your specific device model!
Frequently Asked Questions
Why does my Samsung phone say "Failed to read data" when I open Supplementary Services?
This error occurs when your device times out while attempting to query your carrier's servers for your line's feature configuration. It is commonly caused by active Private DNS profiles blocking the query, weak cellular coverage, or temporary carrier server maintenance.
Will dialing *43# cost money or use my plan's data?
No. Star codes (MMI commands) like *43# are free, standardized cellular commands transmitted directly over basic signaling channels. They do not consume mobile data or incur additional charges on major US cellular networks.
Does Call Waiting work when using Dual SIM or eSIM on Samsung Galaxy devices?
Yes, but both lines must be configured properly. Navigate to Settings > Connections > SIM Manager and verify that both lines support Supplementary Services. Additionally, enable Auto data switching so your phone can route background network queries for Line 2 while Line 1 is actively on a call.
Why does Call Waiting send callers straight to voicemail without ringing?
This usually occurs when Wi-Fi Calling encounters packet loss during handovers, or when a carrier call security app (like Verizon Call Filter or AT&T ActiveArmor) flags the second caller as potential spam and automatically redirects them to voicemail.
Will resetting my mobile network settings delete my personal files?
No. Resetting mobile network settings only clears saved Wi-Fi networks, paired Bluetooth devices, cellular APNs, and temporary network caches. Your photos, contacts, messages, apps, and personal files will remain untouched.
