No gsm after battery change but have wifi

I changed my Ipad 2 battery although it must've been incompatible because Ipad kept rebooting and a message popped up saying "Restore Needed Iphone cannot make or receive calls. Restore from Itunes...". So, I put old battery back in (it was fine except doesn't hold charge as long as it used to and takes longer to charge). The restore message still periodically pops up and I now have to GSM signal. I was meticulous with taking apart my ipad, have all the proper tools and am very familiar with the procedure having done it countless times. I didn't want to restore because I was hoping it was a battery issue and waited for a replacement battery from the company I purchased the battery from. Again, same issues with rebooting so I sent it back and am just using original battery. Here is everything I've done so far with no luck: checked SIM card and it works in another Ipad so I know that's not the issue, I replaced both left and right antennas, cleaned all the contacts for the antennas, restored from a backup (I don't want to do a total restore since I'm Jailbroken and am afraid it won't work and will be left with same problem and no Jailbreak), I verified my account with AT&T and even did the Restore Network Settings several times--as well as the trouble shooting with the SIM card that's posted everywhere and trying different SIM card.

I have wifi and Bluetooth, but in Settings/About the Network shows "not available", cell number shows unknown and modem firmware is blank.

I'd gladly do a full restore if I know it will resolve my issue. Can anyone help me? Thank you!