For really low usage and a slow as a turtle data transfer (2.4 kb rate) go for a basic quality handheld phone. You get good voice quality (there will be about a half a minute delay while the satellites do their work) but know there will be dropped calls after three to fifteen minutes. This level of phone is for short communications. For longer calls of better quality, upgrade. Make sure you ask for call and battery duration, so it will fit your particular needs.
Consider upgrading if you are involved in longer calls (over three hours) requiring higher quality reception (although a longer delay in your reception). You get a laptop sized case with the phone and an antenna as well as a cable to allow phone conversation at a distance from the actual antenna and transmitter. This type of satellite phone is meant for the high use business traveler or those involved in industries operating in countries where there are little or no other options. However, the data transfer is still at 2.4 kb. Renting this phone setup is about $300 a month with a $3 per minute calling cost.
If you are transmitting a ton of data anything less than the 64 kb per second option of the higher quality satellite phone doesn't make sense. These guys are expensive (think $7 per minute while those pesky little kilobytes and hopping from satellite to satellite) and meant for high "in the field" applications. The military are prime for this type of phone.
Like cell phone companies, the satellite service provider often offers phones as well as the service in a neat little package. Do some comparing of services and rates to come up with the least expensive plan covering all of your needs. If you don't intend to hook it up to a computer to send data and don't need to talk for long, then there is no need for the latest word in satellite phones. Consider a prepaid calling card and free email as some options.