A few questions,
So at the AT&T store they tried their sim and got 3 bars at the AT&T store?
You tried your card at the att store and go no bars? and 3 different Soms got no bars? At the store or away from the store or where?
Are the Sims AT&T sims?
Do you get an AT&T signal at your house?
Is the Sim card bad?
Its seems to me that If AT&T used a one of their SIMs and got a signal, that means the phone is ok. All the numbers sound right off the tomp of my head.
So If AT&T used a card that got a signal
-The phone is working (nothing wrong with its fuctions or firmwares)
-They have signal at their shop (probably a micro cell in back)
So, if you tried your SIM in the AT&T store where there is a known signal. then that would most likely mean something wrong with your card.
Ask AT&T to cook you up a new card.
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If you did not try your SIM at the store where there is a known signal, and tried it elsewere, then perhaps the area you are trying it in has no signal.
Go to a location with a known signal and try again.
Those are the only things I can come up with with the info you gave. There seems to be nothing wrong with the phone since AT&T got it to work ( I suppose it is possible tho). It is possible to hack, and mess around with the phone and then "reset" it back to stock (sort of)... but if you trust your buddy.. Most likely there is something wrong with the card(s) you are trying, or there is no signal in the area you are trying it in.
If you can give more specific info on who, what, where, when, how, maybe we can help more.
