Xiaomi Calls Keep Dropping on O2 in London

Xiaomi Calls Keep Dropping on O2 in London – UK Fix

This guide helps if your Xiaomi calls keep dropping on O2 in London, especially in older buildings, flats, or areas with weak indoor coverage.

Quick Answer:
If your Xiaomi calls drop on O2 in London, first check VoLTE is enabled – Settings → SIM cards & mobile networks → O2 SIM → VoLTE → ON. Then enable WiFi Calling to route calls over your broadband when signal is weak. If calls still drop, switch to 4G (not 5G) – Settings → SIM cards & mobile networks → O2 SIM → Preferred network type → select 4G/3G/2G auto.

Applies to Redmi, POCO and Xiaomi Phones

This guide applies to Xiaomi, Redmi and POCO devices running MIUI or HyperOS on the O2 UK network, including MVNOs like Giffgaff, Sky Mobile, and Tesco Mobile.

🔍 Quick Diagnostic Table

What you see	What it usually means
Calls drop indoors but work outside	Weak indoor coverage or Band 20 issue
Calls drop only in certain areas of London	Local mast congestion or coverage gap
Calls drop when switching between 4G/5G	5G handover issue
Calls drop but data works	VoLTE or IMS issue
Calls drop when phone is idle	Battery optimisation interfering

🔍 Quick Start – Find Your Path

Symptom	Most Likely Cause	Go To
Calls drop indoors but work outside	Weak indoor coverage	Section 1
Calls drop only in certain areas	Local mast congestion	Section 2
Calls drop when switching between 4G/5G	5G handover issue	Section 3
Calls drop but data works	VoLTE or IMS issue	Section 4
Calls drop when phone is idle	Battery optimisation	Section 5

Section 1 – Calls Drop Indoors but Work Outside (Most Common)

If calls drop indoors but work fine outside in London, one of the most likely causes is weak low-band LTE coverage (such as Band 20 (800MHz)), although indoor coverage also depends on your local O2 cell configuration. O2 commonly uses Band 20 alongside other LTE bands for indoor coverage in London. Older buildings with thick walls can block this signal.

Try these in order:

1. Check O2 coverage map – Visit O2's website and enter your London postcode. Coverage maps provide estimates and may not reflect indoor performance inside every building.
2. Enable WiFi Calling – Settings → SIM cards & mobile networks → O2 SIM → WiFi Calling → ON. This routes calls over your broadband when signal is weak, if your O2 account and handset support WiFi Calling. If WiFi Calling won't enable, see our Xiaomi WiFi Calling Not Working on O2 guide.
3. Check VoLTE is enabled – Settings → SIM cards & mobile networks → O2 SIM → VoLTE → ON.
4. Switch to 4G – Settings → SIM cards & mobile networks → O2 SIM → Preferred network type → select 4G/3G/2G auto (not 5G). 5G can be weaker indoors.
5. Check if your phone supports Band 20 – Most UK Xiaomi models include Band 20. Imported models intended for other regions may not support all UK LTE bands.

Section 2 – Calls Drop Only in Certain Areas (Local Congestion)

O2's network may experience temporary congestion in busy parts of London, particularly around transport hubs, shopping districts or major events. Calls may drop when many users are connected to the same local cell.

Try these in order:

1. Switch to 4G – Section 1.
2. Move to a less crowded area – Even moving a short distance may allow your phone to connect to a different cell sector or nearby mast.
3. Test at different times – If calls drop during peak hours (9am-6pm) but work at other times, congestion is the cause.
4. Enable WiFi Calling – If you're in a building with WiFi, use WiFi Calling.

Section 3 – Calls Drop When Switching Between 4G and 5G (Handover Issue)

If calls drop when your phone switches between 4G and 5G in London, the issue is likely 5G handover instability.

Try these in order:

1. Switch to 4G – Section 1. Forcing 4G avoids 5G handovers, which may improve call stability if handovers are causing the problem. See our Xiaomi 5G Keeps Disconnecting UK guide if you still have issues.
2. If available, check 5G SA mode – Very few Xiaomi devices expose SA/NSA controls. If your device provides advanced 5G mode options, try switching from SA to NSA. Most Xiaomi phones do not expose this setting.
3. Check O2 5G coverage – 5G in London can be patchy. If 5G is weak, your phone may constantly switch between 4G and 5G.

Section 4 – Calls Drop but Data Works (VoLTE or IMS Issue)

If you have signal and mobile data works, but calls drop, the issue is likely VoLTE or IMS registration.

Try these in order:

1. Check VoLTE is enabled – Settings → SIM cards & mobile networks → O2 SIM → VoLTE → ON. If VoLTE isn't available, see our Xiaomi VoLTE Not Working on O2 guide.
2. Check IMS registration – 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.
3. Toggle Airplane mode – ON for 30 seconds, then OFF. This forces IMS re-registration.
4. Enable WiFi Calling – Section 1.

Section 5 – Calls Drop When Phone Is Idle (Battery Optimisation)

If calls drop when your screen is off or phone is idle, battery optimisation may be interfering. Battery optimisation is a less common cause, but it can affect background network behaviour on some devices. See our Xiaomi Battery Saver Affects Mobile Network guide for more details.

Try these in order:

1. Turn off Battery Saver – Settings → Battery → Battery saver → OFF.
2. If available, remove battery restrictions for Phone/Network services – Settings → Apps → Manage apps → search for "Phone" → Battery saver → Set to "No restrictions".
3. If available on your version of HyperOS, disable "Clear cache when device is locked" – Settings → Battery → Additional features → Clear cache when device is locked → OFF.
4. Switch to 4G – Section 1.

Why Do Calls Drop on O2 in London?

• Weak low-band LTE coverage (most common) – O2 commonly uses low-band LTE bands (such as Band 20 (800MHz)) alongside other LTE bands for indoor coverage. Older London buildings with thick walls can block this signal.
• Local mast congestion – O2's network may experience congestion in busy parts of London.
• 5G handover instability – Switching between 4G and 5G can cause calls to drop.
• VoLTE or IMS issue – Calls may drop if VoLTE is disabled or IMS registration fails.
• Battery optimisation – Can interfere with background network services.
• Temporary network congestion or engineering work – May also affect call stability, particularly during busy periods.

⚠️ What NOT to Do

• Don't factory reset your phone – This is rarely needed for call drop issues.
• Don't assume your phone is broken – Test your SIM in another phone indoors to see if the issue persists.
• Don't ignore WiFi Calling – It's the most effective fix for indoor call drops.

Quick Questions

Why do my calls drop indoors on O2 in London but work outside?
O2 commonly uses low-band LTE bands (such as Band 20 (800MHz)) alongside other LTE bands for indoor coverage. Older London buildings with thick walls can block this signal. Enable WiFi Calling to route calls over your broadband.

Does WiFi Calling fix call drops in London?
Yes. WiFi Calling routes calls over your broadband, completely bypassing mobile signal issues indoors, provided your O2 account and handset support WiFi Calling.

Why do calls drop only in certain areas of London?
O2's network may experience temporary congestion in busy parts of London. Switch to 4G or move to a less crowded area.

Why do calls drop when switching between 4G and 5G?
5G handover can be unstable in some areas. Switch to 4G for more stable calls.

Will resetting network settings help?
It can help if settings are corrupted, but WiFi Calling and VoLTE are usually more effective for call drops.

Does O2 support WiFi Calling on Xiaomi?
O2 supports WiFi Calling on many compatible Xiaomi devices, although availability depends on your handset model, software version and account provisioning.

Why does my Xiaomi show full signal but calls still drop?
Signal bars only represent the strength of the radio signal. They do not guarantee reliable voice calling, as VoLTE, IMS registration, or network congestion can still affect call quality. Check that VoLTE is enabled, confirm IMS registration if your device supports it, and enable WiFi Calling where available.