US GSM Carrier Unlocked Sprint Touch Pro 2 - Data Issue

[TOOL1075]

I unlocked my Sprint Touch Pro 2 and I am using an AT&T SIM card here in the United States successfully.

The first few times I used GSM mode, a menu would pop up and ask me which network settings I wanted to use (AT&T or T-Mobile).

Now, that menu is no longer popping up. So, I am unable to select the settings for AT&T. Data is now not working on GSM (the phone tries to dial #777 as if it is connected to Sprint).

How can I get that dialog box to pop back up and prompt me to pick the carrier settings? I'm assuming that is what will fix it.

Thanks for the help.