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Galaxy S2 'not registered on network'

I have had my phone for several months, on an O2 monthly tariff. About once per week the connection to O2 goes AWOL. Texts in or out and calls in or out are met with a refusal because I have no connection to a network (i.e. O2). There is plenty of signal, and it refuses to search for any operators. The 'solution' is a reset of the phone, complete switch off or a warm reboot. The problem is that it is only when I notice that there are no incoming calls that I see the problem and some of the missed calls were important. BTW, I have updated to Android 4.0 via the approved website and the problem still exists.

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Registered: ‎04-04-2012

Re: Galaxy S2 'not registered on network'

Did you do a factory reset and clear your cache?
I have no affiliation whatsoever with O2 or any subsidiary companies. Comments posted are entirely of my own opinion. This is not Customer Service so we are unable to help with account specific issues.

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OnePlus 6 (O2 & Sfr), Z3 Tablet (Three UK), iPhone 8+ (EE)
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Registered: ‎06-04-2012

Re: Galaxy S2 'not registered on network'

Check your SIM is working OK by removing it and cleaning out inside the handset. A factory reset and cache clear shouldn't affect the SIM itself. The appropriate settings should be inherited from the network after replacing the SIM. Unfortunately many of these Android telephones have no bootloader/fastboot menu's anymore.
Leave your candy-colored cans in the toy chest and try a pair of proper headphones.