and up the east coast ( to NC so far) the only spot we had zero coverage was deep in the Ten Thousand Islands area of Florida. Little Shark River to south of Everglades City.
We even had Internet anchored on the Gulf side of Ship and Horn Islands on Mississippi Sound. Weak, but useable.
The nav function of course worked crossing the gulf.
We didn't use the phone part in the Bahamas due to cost per minute, using a Batelco calling card or Skype instead.