On March 22, BB posted that he'd be fishing the Chandeleur Islands, which this articles states is 40 miles off the Mississippi coast.
http://www.sportfishingmag.com/fishing-chandeleur-islands?image=0&wJwhAJEk1zvRQB6L.01
Assuming BB uses AT&T Wireless, per the search warrants, AT&T has coverage in the Gulf of Mexico:
http://www.wireless.att.com/learn/international/roaming/faq.jsp
AT&T has a roaming agreement with Petrocom, which, as far back as at least 1998, has provided cellular service in the Gulf of Mexico. "PetroCom covers 68,000 square miles of Gulf, from lower Mobile Bay, Alabama, to Brownsville, Texas, and extending 150 miles offshore."
http://magazines.marinelink.com/Mag...806/content/petrocom-completes-service-201324
http://www.advantagecap.com/advantage-invests-1-45-million-in-petrocom-of-louisiana/
Some AT&T customers shared on AT&T's troubleshooting pages that cell phone bill would show charges from Petrocom.
This article says that there are cell towers on offshore oil rigs.
http://www.rigzone.com/training/insight.asp?i_id=337
FWIW, it looks like BB would have been accessible by cell phone in the Gulf of Mexico.