Xiaomi WiFi Calling Not Working on O2 UK Fix

Xiaomi WiFi Calling Not Working on O2 UK Fix

If your Xiaomi, Redmi, or POCO device shows the WiFi Calling (VoWiFi) option is enabled, but calls still drop or fail to connect over WiFi, this guide explains why and how to fix it. This article focuses on cases where the option exists but doesn't work properly, rather than cases where the option is missing.

Quick Answer:
If WiFi Calling is enabled but not working on O2, first check that Airplane mode is OFF and you're connected to a stable WiFi network with internet access. Then go to Settings → SIM cards & mobile networks → O2 SIM → ensure WiFi Calling is ON and VoLTE is also ON. Contact O2 to confirm WiFi Calling is provisioned on your account and your IMS registration is active.

🔍 Quick Diagnostic Table

What you seeWhat it usually means
WiFi Calling toggle ON but calls fail over WiFiIMS registration issue or weak WiFi signal
WiFi Calling works but disconnects frequentlyRouter settings, VPN, or battery optimisation interfering
WiFi Calling works on some WiFi networks but not othersRouter or firewall configuration
WiFi Calling works after Airplane mode toggleTemporary IMS registration glitch
WiFi Calling works for a few minutes then stopsBattery optimisation or unstable WiFi connection

Why WiFi Calling May Not Work on O2

WiFi Calling (VoWiFi) uses IMS (IP Multimedia Subsystem) registration to route calls over a WiFi network. Several factors can prevent it from working correctly:

  • IMS registration failure – Your phone may not be properly registered with O2's IMS servers, even if the toggle is ON.
  • Carrier provisioning – WiFi Calling may not be fully provisioned on your O2 account or SIM profile.
  • WiFi network issues – The WiFi network may not be stable enough to support calling, or it may block the necessary traffic.
  • App conflicts – AdGuard and other VPNs can interfere with IMS registration.
  • Battery optimisation – HyperOS may be restricting background processes needed for WiFi Calling.
  • Router or network configuration – Some routers can sometimes affect WiFi Calling. If WiFi Calling works on another WiFi network, the issue is likely related to the original network or router configuration.

Fix 1 – Check IMS Registration

IMS registration is the core requirement for WiFi Calling. If your phone isn't registered with O2's IMS servers, WiFi Calling won't work. If IMS isn't registered, see our Xiaomi IMS Not Registered – UK Fix guide.

Try these in order:

  1. Check IMS registration status – If your device supports the Phone Information menu, dial *#*#4636#*#* → Phone information → look for "IMS registered". If false, the phone isn't registered for voice services. This menu is not available on all devices.
  2. Toggle Airplane mode – ON for 30 seconds, then OFF. This often prompts the phone to re-register with the IMS service. Reconnect to WiFi afterwards if it doesn't reconnect automatically.
  3. Restart your phone – A full reboot can resolve temporary IMS registration glitches.
  4. Check mobile data is enabled – IMS registration on O2 may require mobile data to be switched on, even while you're connected to WiFi.

Fix 2 – Check O2 VoWiFi Provisioning

If IMS registration is failing, O2 may not have WiFi Calling correctly provisioned on your account.

Try these in order:

  1. Check your account – Call O2 (202) or use the O2 app. Ask: "Is WiFi Calling correctly provisioned on my account? Can you refresh my SIM or eSIM profile?"
  2. Check SIM age – If you're using an older SIM that predates O2's WiFi Calling rollout, your carrier may recommend a replacement SIM.
  3. Enable VoLTE – Settings → SIM cards & mobile networks → O2 SIM → VoLTE → ON. WiFi Calling and VoLTE often share IMS infrastructure, so enabling both can help.

Fix 3 – Check WiFi Network and Router

WiFi Calling requires a stable WiFi connection and a network that allows IMS traffic to pass normally.

Try these in order:

  1. Check WiFi signal strength – If you have only 1-2 bars of WiFi, try moving closer to the router or testing on a different network.
  2. Test on a different WiFi network – If WiFi Calling works on another network, the issue is with your router.
  3. Restart your router – Power off your router for 30 seconds, then power on and reconnect your phone.
  4. Disable WiFi power saving – Settings → Connection & sharing → WiFi → Advanced → turn OFF "WiFi power saving" if available.

Fix 4 – Check for App Conflicts (AdGuard, VPN)

AdGuard and other VPNs can interfere with IMS registration.

Try these in order:

  1. Disable AdGuard or any ad-blocker temporarily – Some ad-blockers prevent WiFi Calling from activating, especially when reconnecting to WiFi.
  2. Disable VPN – If you're using a VPN, try turning it off and reconnecting to WiFi.
  3. Restart your phone – After disabling these apps, restart and test WiFi Calling.

Fix 5 – Check HyperOS Battery Optimisation

HyperOS may restrict background processes needed for WiFi Calling.

Try these in order:

  1. Turn off Battery Saver – Settings → Battery → Battery saver → OFF.
  2. Remove restrictions for Phone/IMS services – Settings → Apps → Manage apps → search for "Phone" → Battery saver → Set to "No restrictions". If your device exposes these services, also check for "IMS" or "WiFi Calling" services.
  3. Disable "Clear cache when device is locked" – Settings → Battery → Additional features → Clear cache when device is locked → OFF.

Fix 6 – Reset Network Settings

If none of the above work, resetting network settings can resolve corrupted configurations.

Try this last:

  1. Reset network settings – Settings → Connection & sharing → Reset Wi-Fi, mobile networks, and Bluetooth (removes saved Wi-Fi passwords).
  2. Restart your phone – After resetting, restart and reconnect to WiFi.
  3. Wait a few minutes – IMS registration is not always instant. Allow 2-3 minutes for registration to complete before testing.
  4. Re-enable WiFi Calling – Settings → SIM cards & mobile networks → O2 SIM → WiFi Calling → ON.
  5. Test WiFi Calling – Place a call while connected to WiFi.

Common Causes Recap

  • IMS registration failure (most common) – The phone isn't connected to O2's IMS servers. This often resolves with Airplane mode toggle.
  • Carrier provisioning – WiFi Calling may not be enabled on your O2 account or SIM profile.
  • Router or network configuration – Some routers can sometimes affect WiFi Calling.
  • WiFi stability – Weak or unstable WiFi can prevent WiFi Calling from working.
  • App conflicts – AdGuard, VPNs, and some ad-blockers can interfere with IMS registration.
  • Battery optimisation – HyperOS may restrict background processes needed for WiFi Calling.

⚠️ What NOT to Do

  • Don't factory reset your phone – This is rarely needed for WiFi Calling issues.
  • Don't assume O2 doesn't support WiFi Calling – O2 supports WiFi Calling on many Xiaomi devices. The issue is usually provisioning, router, or IMS registration.
  • Don't ignore your WiFi network – Router configuration can sometimes affect WiFi Calling.

Quick Questions

Why is WiFi Calling enabled but not working on O2?
The most common cause is IMS registration failure. Toggle Airplane mode on/off to force re-registration. If that doesn't work, check your O2 account provisioning.

Does O2 support WiFi Calling on Xiaomi?
Yes, O2 supports WiFi Calling on many Xiaomi devices. You may need to contact O2 to ensure it's provisioned on your account.

Can a VPN stop WiFi Calling from working?
Yes. VPNs and ad-blockers can interfere with IMS registration. Disable them temporarily to test.

Why does WiFi Calling only work on some WiFi networks?
Your home or office router may be interfering with WiFi Calling traffic. Test on a different network to confirm.

Will resetting network settings fix WiFi Calling?
It can help if settings are corrupted, but try the simpler fixes first – resetting removes saved Wi-Fi passwords and Bluetooth devices.

Why doesn't the WiFi Calling icon appear?
Some Xiaomi devices only show the WiFi Calling icon when the phone has successfully registered with the carrier's IMS service and is actively ready to place calls over WiFi. The exact behaviour varies by HyperOS version and carrier configuration.

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