Well I woke up this morning and turned on my phone (I turn it off at night cause it keeps me up with the redlight) and this morning when I woke up it said 'sim card error' and yeah it is pissin me off

has it been always like that? Unlock it through various method (you can find some here)

And.. check with AT&T if your SIM is valid! Or even if the phone accepts ur sim card.

it worked for the first 3 months iv had the phone