My phone will read my AT&T sim card and the bands all match, but it will not connect to my network for phone, SMS or internet.
Is there a possible software issue on the phone side?
After checking other forums I'm not the only one with this issue.
If bands are the issue, there are no carriers in the USA that will connect to this phone. AT&T matches the frequencies more than any other carrier in my country.

If your local carrier provides one of this bands in your area but you get no connection please check the APN settings. If this don't help please ask the Carrier-Service for help.

GSM Mode: EGSM900, DCS1800, PCS1900, GSM850
UMTS Mode: WCDMA-IMT-2000, WCDMA-GSM-900
LTE Mode (only for SIM1): Band 1,3,7,8,2