The phone should support both the 850 & 1900 MHz bands to work well on AT&T Mobility's network. Some of the phones that T-Mobile has sold in the past only support the 1900 MHz band, which will not work at all in 850 MHz only coverage areas. There is also a possibility that you are in a poor coverage area. It may help to know the make & model of the phone that you're using, if you've tried other phones in that area, and a zip code. Have you tried AT&T's Coverage Viewer to find out what your coverage area is or Wireless Advisor to find out which bands are supported in your area?
shawnta2000 wrote: i got a phone that is tmobile but its unlocked to work on at&t but the emails dont come to my phone it saids there is insufficent network coverage what does that mean thanks
Phones crippled (I'm sorry, I meant "customized") by a carrier often have their data settings hard coded to that carrier's settings. SIM unlocking the phone doesn't necessarily unlock the data settings as well, it may require that you replace the T-Mobile customized firmware with a generic version.
Even if the data settings are unlocked, you would have to set them manually for AT&T, as they're not automatically configured via the SIM. My best guess based on what you're saying is that your phone is trying to use T-Mobile data settings, which of course fails, so it thinks you have no data (GPRS/EDGE) coverage.