AT&TGSM vs. TMO in Baltimore County

[TechnoMetrics]

My 720 finally bit the dust is now in 2 pieces. TMO won't budge on their price for the V300 which IMO is total junk. Their not getting the V600 for another month and even then their going to want 4 bills for it...F that. I am not partial to TMO and will gladly jump to ATT to get the V600 or even the Nokia 6820 (even though I dont like Nokia) at a great price. However there is this glaring spot directly over I-83 just about at the PA/MD border that looks like they have no coverage. No one in the store or at customer service can confirm or deny if its covered, they just say that they have a 30 day money back. Well I'm not going thru the trouble of porting my number, then back if it sux.

I've searched and searched and cant find any direct comments on ATT in Baltimore County or York PA. Any help would be greatly appreciated...and yes that spot is important to me as I drive thru it everyday