Getting all of the settings correct for attaching your ATT GSM sim card to the network can be difficult. And it is a moving target.
For most data collectors, my ‘leave everything blank’ solution seems to work fine. For the Handheld Nautiz X8, I have found that I need to enter a bit of extra information.
Here are the details [ NautizX8_ProvisioningATTSIMCard ] …
You mileage may vary depending on your local network.
One hint, if your GSM sim card does not work out of the box, you might ask your ATT support person to provision the card just like mine. Say “Mark Silver’s card is known to work, his phone number is 801-652-9320”. The ATT agent will resent you telling them this and they will complain, but when they look up the provisioning information for my card, they will find some 4-digit code that they add to your card and it will begin working.