AT&T sim card not working in AT&T phones?

I had a contract with AT%26amp;T which has now expired, so this is how i got my phone (LG Xenon). well I wanted another number (meaning another sim card) so I could let my mother use the once contracted sim card in my other phone i have (Iphone) and i could just use a prepaid sim card in my xenon. So i went and bought a cheap go phone, just for the sim card, and activated it. The sim card will only work in the phone it came with, not in my xenon, Iphone, nor a friends samsung ,who buy the way has a AT%26amp;T prepaid sim card too (whos sim card will work in both of my phones). When the sim card is in either phone signal bars will be displayed, but in the Iphone when I try and make a call or txt, it says it can't connect to the network. And for the Xenon when I try to open my contacts it says 'sim card not ready' and when i try to either write a message or open my inbox it says 'sim card initalizing...%26quot;

I've restarted the phone, even taken the sim card out, but nothing changes. I don't want to be stuck with a cheap go phone when I should be able to just switch the sim card. And I don't think the phone is locked because it's not like I'm trying to use a different network's sim card.

Any help at all would be greatly appreciated. :)AT%26amp;T sim card not working in AT%26amp;T phones?
Does that gophone sim look like this?

http://cgi.ebay.com/AT-T-GoPhone-New-GoP



This is one of the notorious new orange/white Att Gophone sims which will lock itself to ONE PHONE ONLY for six full months . Att started doing this about three months ago. It sucks but this is a new one. My argument is , what if you BREAK the original phone , the only one it will work in before the six months are up? Then what?



The best way to do this is go to a Att corporate store , tell them that you broke the Gophone that it came in and threw it away, could you please give me a new (Regular ) sim that will work in my xenon? Have them transfer the contents of the orange/white crap sim to the regular good one so you don't have to wait six months.



Good luck.