In my area of N Colorado, there's very little cell coverage. It's simply a terrain and distance issue, high mountains and deep canyons, and cell doesn't work in the canyons.
I wrote an interesting article in Back Home magazine a couple years back on the topic. Here's some tips in a nutshell:
When cell phone shopping, buy one with an external antenna jack. These are getting harder and harder to find. But it lets you attach a high-gain cartop antenna, and if you have an extra $300 lets you also attach a (totally legal) booster that bumps your transmit power from 1/2 watt to 3 watts (the legal max). These 2 steps can make a huge difference in your coverage, and the cartop antenna is cheap. Without an external antenna jack, there's still a slip-on, magnetically coupled adaptor you can use, but there are some losses. You can check with [url=http://cellantenna.com/:e8be1]http://cellantenna.com/[/url:e8be1] before purchase to find out if there's a slip-on adaptor avaialble for a phone model that has no external jack. They can also fix you up with boosters and high-gain antennas.
Since I fish with a buddy that has a pacemaker and with my 75 year old Dad, we carry FRS walkie talkies, and we only buy the kind that can take alkaline batteries in addition to rechargables.
I also keep a handheld ham radio in the truck because of the large number of mountaintop repeater sites around the country, a ham license is a GREAT idea for any outdoorsperson, and is easy to get -- the test is quite simple to get a license (you have a 1 in 4 chance of passing even if you don't study!). ;~) Many ham repeaters have 911 phone patch capability built in, talk to your local ham radio club to find out 911 patch info for your area. A good, handheld ham radio costs only $100.
I don't carry the ham radio with me on the river or lake because---I'm a firefighter and medical responder, and thanks to a post-9/11 FEMA grant everyone in our department has a handheld Police/Fire radio, so I can get help faster that way. Never had to use it for a *fishing* emergency, but surprised the s*** out of some folks with an illegal campfire last year when the ranger pulled in 10 minutes after I told them to put it out, and they told me to stick it up my....
Anyway -- you CAN improve your cell coverage, and if you fish with anyone who might have health problems, a ham license is a great idea--our local ham repeaters have people listening in 24/7 who are more than willing to call 911 for you from a landline, if there's no phone patch.
PS at the time I wrote my article, Globalsat et al was way too expensive for most people. Prices are dropping now, and some sat phone providers have 'emergency only' packages that are much less expensive.
[This message has been edited by danbob (edited 16 July 2006).]