For those of you who don't know, sat phones do suffer from the problem of needing a 'line of sight' to the satellites. It has been my experience that they work poorly in urban areas/canyons, worse than a GPS unit. When in an urban area you will end up finding all the best roof top bars to make calls. The also tend to be much more sensitive to 'atmoshperic conditions' than other wireless communications but that could have just been my phone though I was three miles closer to the sats than at sea level.
What ever phone/plan you go with, try to find one with free text messaging so you can recieve info from home. This saves battery life and expense of checking the voice mail. For those 'weekend warriors' go with a plan where you buy pre-paid minutes and pay the premium so that they can roll over. Consider buying a refurbished unit instead of renting if you see several years of multi month usage in your future.
Buy two batteries if you can even if you will be near a power grid at times. The reason I say this is unless you are in your personal vehicle, you cannot vouche/predict how operational the vehicle is you will be driving in. A number of times I have been in vehicles where the 12V cig lighter doesn't work. On an 8 week field season I didn't even run down the charge of one battery, but I only had it on for about 15-20 minutes a day and only had about 2-3, 10-20 minute phone calls per week.
People I work with have also reported good luck with solar chargers for recharging batteries.
Have fun,
Ross
