I have had very good coverage with Sprint on the East Coast
of the U.S. My phone
is the finest of technology from 1913 (well, it's pretty old anyway), a palm Treo (yes, it still works well!). I was getting a reliable signal two to three miles out. I was able to use voice and data.
Please note that this distance will vary depending upon where on the coast you are. For example, there are some areas just north of the entrance to the Chesapeake that the distance from shore drops quite a bit and in a very few spots, I couldn't get any signal for ten or fifteen minutes while traveling at five knots. This was because the shore was mostly marshland and there were no towers nearby.
Overall however the signal was pretty good with Sprint down the coast. I should also point out that going up the Delaware, through the C-D canal, and down the Chesapeake I have had no problems with signal.
Laser, thanks for the heads up about Republic Wireless. I will check them out. Do you know if they use their own network or piggyback off of someone else's network, and if so, do you know which one?