[AC Question]

I bought a Galaxy S4 from carphone warehouse which is unlocked , but ever now and again it says (mobile network will be unavailable until you restart with a valid sim card inserted ) I have a 02 sim card in it and it switches on and works

[belodion]

It may be a bad SIM or a problem with the SIM tray. Take it to O2 and ask their advice.
Also, a Cache Partition wipe may be worth trying.

Posted via the Android Central App

[Jazz S1]

Hi
I am a new guy at it also and my s4 started saying restart sim i tried rebotting etc and was going to get some to root it etc as it was driving me crazy
But i kept looking at all solutions until i was came acrossa guy who cleaned the sim and sim boot with rubbing aclhol i had some of the spray bottle of rubbing alchol right next my computer i opened the phone took the sim out sprayed 2 squirts of rubbing alchol and and blew the excess out right away i inserted the Sim and its as good as new
I had asked my indian enginess friend they said change the sim slot etc etc
Anyway i was so lucky i dont know but it worked for me