Can I purchase an AT&T go phone sim onling, activate it, & then put it in any ATT phone? I have an HTC fortress & I was wondering if that would work?
I will add one comment to hme83's. File it under "to be tested", though.
The HTC Fortress (aka. HTC Touch Pro2???) is probably assumed by AT&T to be running the OEM WM6.x (and not Android). If so, the HTC Fortress might not be assumed to be a smartphone, and you might get away with the $50-mon unlimited talk/text/data plan. [Obviously, if a data plan beyond simple texting has your interest.]
This because "smartphones" are classified by AT&T as "smart" only by their OEM OSes (one of: Android, iOS, Blackberry and WM7). WM6.x smartphones may not be considered "smartphones" for the purpose of the (pre-paid) data feature plan.