I've got a user who has a Blackberry 7230 which does not do GSM 850. He works in Amarillo, Texas (79120) and Pampa, Texas (79065)

He's been complaining about coverage. Amarillo looks ok (not great, just ok) and Pampa is listed in a checker-board pattern that says (Extended digital roaming) So I jumped over to Cingular and keyed in the zip code for Pampa and it replied back "No Coverage"... So if it is not Cingular and not T-Mobile, who's servicing the area? I'm probably going to have to move him to a different carrier, but I just am not sure at this point. I prefer GSM or Nextel because of the SIM cards. I could do verizon but even their coverage lists that there may be analog pockets which the BB can't do.

Anyway to tell who's running the towers?

not unless you have the camping feature on you phone will you be able to tell. the camping feature has to be programed in the phone by the engineer of a cell company or tower company and it will only pick up the same signal as your provider (CDMA, GSM etc.)