help: com.android.phone error

[neonflash]

i have 2 phones one i us most of the time one is for drunk nights out etc bc i dont want my other one to get lost damanged stolen.
the 2nd phone is lg optimus black p970.
its been working 100% fine.
i havent used it for about a week.
tongiht i go to use it and keep gettin the com.android.phone error. & the signal drops.
i have NO IDEA why.
i use the same sim in both phones so just take it out phone 1 and put into phone 2 when i decide to use the other.
i havent updated anything new (apps) i have updated the software or anything.
a week ago i powered it off and it had been working fine. all i did tonight was power it on, went to send a text and it gives me that error. the same with whatapp. dl'ing apps works.
any idea what it could be & why its happened? how to fix?

 

[neonflash]

i'm on O2.
tried the phone with another sim (also o2) and it works fine.
but i dont understand because i have used the phone with my usual o2 sim card before like 1 week ago.
powered the phone off with that sim inside. used the sim in another phone for 1 week now put it back in lg and power on and get that error.

 

[neonflash]

just wanted to bump this. seems no one can find a solution i've searched the net high and low.
i got a new sim card from my network provider but still getting the same error.
i've tried factory resetting the phone and still get the error.
i dont understand why its only that sim card. the sim works fine in my other 2 phone but on the other hand every other sim i've tried (a different o2 one,t-mobile & orange) all work in the phone that gives me the error with my usual sim.
i cant determine is it the phone or the sim. the sim works wiht other phones, the phone works with other sims :$
could it be my phone number causing the problem.