Telecom Troubleshooting & Mobile Network Help

Mobile data failures on UK networks are usually caused by one of four things: mobile data toggled off, an incorrect APN setting, an account restriction (spending cap or unpaid bill), or a temporary network outage. Start by toggling mobile data off and on, then restarting your phone. If that fails, check your APN settings match your carrier's values.

On Android, go to Settings → Network & Internet → Mobile Network → Advanced → Access Point Names. On Samsung, go to Settings → Connections → Mobile Networks → Access Point Names. On iPhone, go to Settings → Mobile Service → Mobile Data Network (this field is managed automatically by most UK carriers).

A PAC (Porting Authorisation Code) is a 9-character code (3 letters + 6 numbers, e.g. PAC123456) that lets you transfer your mobile number to a new network. Under Ofcom rules, your current network must provide it instantly when you text PAC to 65075. It is valid for 30 days.

A PAC code is valid for exactly 30 days from the date it is issued. If it expires before you submit it to your new provider, text PAC to 65075 again to get a fresh code. There is no limit on how many times you can request one.

eSIM activation failures are most commonly caused by an expired QR code (they typically last 24–72 hours), a device that is carrier-locked and unable to accept the eSIM, or a provisioning delay on the carrier's side. Request a new QR code from your carrier and ensure your device is eSIM-compatible before trying again.

On iPhone: Settings → General → Transfer or Reset iPhone → Reset → Reset Network Settings. On Android: Settings → System → Reset options → Reset Wi-Fi, mobile & Bluetooth. On Samsung: Settings → General Management → Reset → Reset Network Settings. This removes saved Wi-Fi passwords but does not delete personal data.

MMS requires an active mobile data connection — it cannot send over Wi-Fi alone. Check that mobile data is enabled even when connected to Wi-Fi. Also verify your MMSC settings match your carrier's values. The most common MMS fix is enabling mobile data and correcting the APN/MMSC settings.

First, enable data roaming in your device's mobile network settings (Settings → Mobile Network → Data Roaming). Second, confirm your UK plan includes roaming in your destination — most major UK networks include EU roaming. Third, if no service, select a network manually under Network Operators settings.

No Service means your phone cannot register on any mobile network. Common causes: SIM not inserted correctly, Airplane Mode accidentally left on, being in a no-coverage area, a network outage, or an account suspension. Toggle Airplane Mode, reinsert the SIM, and check your carrier's coverage map for your location.

Incorrect APN settings do not slow data — they prevent data from working entirely. Fixing wrong APN settings restores normal speed but does not increase it beyond your plan's limit. For slow data, the cause is usually network congestion, a fair-use throttle on your plan, or being on 3G rather than 4G.

Signal bars confirm network registration, not internet access. Internet requires a correctly configured APN data gateway. Go to your APN settings and verify the APN value matches your carrier's published settings. Also check your account has no data bar or spending cap applied.

When a hotspot connects but shows no internet, the problem is almost always the phone's own mobile data — not the device connecting to it. Test mobile data directly on your phone first. If mobile data works on the phone, try restarting the hotspot, and verify your carrier plan includes tethering.

5G requires three things: a 5G-capable phone, a plan that includes 5G, and being within 5G coverage. Check your device specs, confirm your plan includes 5G in your carrier app, and use your carrier's coverage checker to verify 5G is available in your current location.

After inserting a new SIM from the same carrier, restart your phone and wait 15–30 minutes for data services to provision. If data does not work after 30 minutes, check APN settings match your carrier's values. If still no service after 1 hour, contact your carrier — they may need to complete provisioning manually.

USSD codes (like *#21# or ##002#) require a live network connection. If they fail, check you have mobile signal and are not in Airplane Mode. Some devices and carriers have limited USSD support — if a code fails, try the equivalent feature in your carrier's app or website instead.

On iPhone: Settings → Mobile Service → Wi-Fi Calling → enable toggle. On Android/Samsung: Settings → Connections → Wi-Fi Calling (exact path varies by manufacturer). Wi-Fi Calling must be supported by both your device and your carrier plan. Not all UK MVNOs support Wi-Fi Calling.

Voicemail works through call divert. If it has stopped, dial **61*[voicemail number]# to re-enable divert when unanswered. Access voicemail by dialling your carrier's voicemail number (123 for EE, 901 for O2, 443 for giffgaff). On first use, follow the prompts to set a PIN.

Use these standard GSM codes from your phone dialler: **21*[number]# to forward all calls; ##002# to cancel all forwarding; *#21# to check forwarding status. If codes fail, check you have network signal and the destination number is in standard UK format (e.g. 07911123456).

Yes, if your device supports Dual SIM Dual Standby (DSDS). Most flagship iPhones from iPhone XS onwards and many Android flagships support simultaneous eSIM + physical SIM. You can set one as primary data and the other for calls, or have both active for calls.

Intermittent mobile data drops are most often caused by weak signal at the edge of coverage, a data limit being reached, background app restrictions on Android, or Low Power Mode reducing connectivity. Check your signal quality, remaining data allowance, and disable any battery optimisation settings for your browser.

Run a speed test first to measure actual speeds. If below 5 Mbps on 4G, check: (1) network type — are you on 3G or 4G? (2) data allowance — have you hit a fair-use throttle? (3) time of day — peak hours (5–10pm) cause congestion. If always slow, check APN settings and contact your carrier.

Emergency Calls Only means your phone can detect a mobile network but your SIM is not being authenticated on it. Common causes: the device is SIM-locked, your account has been suspended, the SIM has failed, or you are roaming without a roaming agreement. Contact your carrier to check SIM and account status.

Roaming voice registration connects before data. Ensure (1) data roaming is explicitly enabled in settings, (2) your plan includes data roaming in that country, and (3) the preferred network type is set to Auto (not 5G Only). Some carriers require a roaming add-on for data even in EU destinations.

APN settings may not save if the device is managed by MDM (corporate policy), the SIM is not active, or an existing APN entry is conflicting. Delete all existing APN entries first, then create a new one. On Samsung, use the three-dot overflow menu to reset APNs to default before manually adding carrier values.

Contact your carrier if: the problem started after a SIM swap or account change; if resetting network settings and correcting APN settings has not fixed the issue after 24 hours; if your account shows active but service is not working; or if you need to check for outages, account restrictions, or SIM replacements.