My general advice in cell phones for rural travel is to get an analog
phone.  You'll have a hard time finding anyone who will sell you one, but
vast parts of the country have only analog service and no digital.
Anywhere more than ten miles from an interstate highway is iffy for
digital.  Easily half of Michigan has only analog cell service.  Some
areas don't even have that.

             _ _
  __ _ _   _| | |  | David M. Brodbeck (N8SRE)              Ypsilanti, MI
 / _` | | | | | |  +-----------------------------------------------------
| (_| | |_| | | | @ cyberspace.org
 \__, |\__,_|_|_| "To the optimist, the glass is half full.  To the
 |___/             pessimist, the glass is half empty.  To the engineer,
                   the glass is twice as big as it needs to be."