I have T-Mobile GSM service...
The route I travel, MASS border up 3 - everett turnpike - 93 - 4 - 28, I get GSM coverage all the way up through Concord and Pittsfield on 28. Coverage stops right about at Barnstead town line.
I get no GSM coverage North of Pittsfield including anywhere on the lake
Someday it will be here!