No signal execept 911 calls

I picked up a mint verizon s3 local on a trade for some scrap phones I had. So here is my issue. I put in a sim(at&t) and got the switch to global notification but it never gets signal. Phone info shows -120dbm 99asu. Figured since it was free I would play with it and installed hyperdriver rls 16 still nothing. Took everything back to the first stock ics nothing. Currently have it on jb 4.1.1 nothing. I started to wonder if the radio was trashed so I dialed 911 with no sim in the phone and it popped up 3 bars and made the call.

Am I wrong in thinking this phone will work on US networks with a sim? Anyone ran into this problem possibly can maybe point me into a direction to get it working. The phone is clean and not blacklisted and it reads the different sims I have put in it I just can't get any signal to pull up other than an emergency call. I know there is signal my s4 is on the gsm network sitting right next to it.

Thanks in advance, I have been searching since yesterday for a solution.

****update.....Went ahead and took it to 4.1.2 stock and happened to find an old verizon sim. Phone picks up verizons network without issue. Still nothing when using the at&t sim.

Sandman-007 said:

It isn't working for AT&T because you haven't set up the appropriate APNs for that network. Google AT&T APNs. Reboot after making the changes. CHECK FOR TYPOS!

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I thought I would at minimum show signal even without adding the apn. From everything I have read its talk ready just inserting the sim. Will look at adding apn's this morning.

Final update. Still no joy on getting it to work and I listed it for sale.