That map with the dots id deceiving. It shows the city centers where ATT 4G is.
I get 4G from just north of Sheboygan, WI, all the way down 43, 94, 294, 80/94 all the way home to Saint Joseph, MI.; 270 solid miles of full coverage. The coverage going west out of Chicago seems continuous all the way past Joliet. I also get 4G all the way up to Grand Rapids, another 90 miles north and east. The 4G never drops off. So that map is deceiving,
I love ATT 4G on my Atrix II droid..
This map on the ATT site shows coverage, and looking at it, coverage is even greater than what's indicated.
Boston seems to be 100% covered - better check your phone and what you are paying for - dark blue everywhere around Boston.
http://www.att.com/network/