With the creation of the SPOT emergency beacon, people have been going deeper into the forest, higher up the mountain, and further out of sight. As emergency rescues and more intense searches are happening with a higher frequency, the need to relay information and not just a "send the cavalry! I NEED HELP!" button is becoming more apparent. With devices such as the DeLorme inReach, you are now able to communicate the actual issue and get updates on ETA's. So, if you break a toe-nail, emergency services won't bill you hundreds of thousands of dollars to get picked up (probably because they will tell you to suck it up and walk out of there). However, if your friend is suffering from hypothermia, they know the tools they need to bring to save their life.
While detailed information is all well and good, it is difficult to give the proper information over 160 character text message. Thus, satellite phones are becoming increasingly popular -- and more affordable. So which is the best? What service do you use? How much is it really going to cost?
Satellite phone technology is in its infancy in terms of consumer use, accessibility, and affordability. SPOT just released their own satellite phone which is the most affordable option on the market to date. However, their network, Globalstar, may not suit your needs. Providing excellent coverage in the North America, their global coverage is not for the globetrotter.
Iridium is by far and large the most extensive and truly global network. Working on the ocean as well as land (Globalstar only works on land) and in every corner of the globe, Iridium is the provider you need for full world travel. However, Iridium is not the most reliable of providers, and is quite expensive (~$1.50/minute). Each provider offers a monthly or annual plan which gives you a bundle of minutes. Get the bundle. Always. This will save you money and the minutes will inevitably get used.
While Iridum and Globalstar are the two most common providers, researching your area of use is imperative. There are smaller companies which only offer service in part of the world which may be cheaper, and more reliable. For example Thuraya and Inmarsat offer great services for certain areas. The smaller companies typically offer more advanced phones as well (which have access to e-mails, etc.) to try and sway you their way.
Depending on which service provider you are using, and where you are going, the antenna is the key to quality service. Unlike a cell phone, the direction it is pointing actually matters. The antenna needs to be extended and point towards the satellite you are trying to connect to (or at least its general area). While sat phones typically work in the most remote areas in the world, they won't work indoors, or near large structures blocking the signal -- so make sure you have a clear view of the sky.
What it comes down to, as is true with any type of gear acquisition, research is key. Find the right product for you, have a clear view of the sky, and keep that antenna pointed up! Also, always carry an extra battery... even if you don't think you'll need it.