Delorme Inreach SE @ 190 grams is a good choice if you are in the market for a PLB or Satellite Phone. It is only slightly dearer (and heavier) than a stand-alone PLB (& so much cheaper than lighter than an Iridium Extreme) but with two way SMS messaging functionality from anywhere on earth. Whenever you send someone an SMS with it your exact GPS location goes with the message. The service is also much cheaper than a satellite phone – from less than $20/month.
NB: Delorme has been taken over by Garmin: https://explore.garmin.com/en-AU/inreach/
You can also load maps on it and use it as a GPS. You can pair it with your mobile phone to make it even more user friendly. It has a tracking function which can notify your friends every few minutes of your exact location (people can even ‘ping’ you to trigger your location) – and of course it has an SOS button which will bring emergency services if you need rescuing. The fact that it has two-way messaging will mean that unnecessary rescues will be reduced enormously.
The internal battery will last a trip up to 10 days (ie over 100 hours), but of course can be recharged on the go eg with one of these: http://www.theultralighthiker.com/charging/ More details here: http://www.inreachdelorme.com/product-info/inreachse.php and here:http://www.theultralighthiker.com/get-lost-get-found-plbepirb/
A PS: The battery will last this long when it has a clear view of the sky and can contact the satellite quickly (usually every 20 minutes). If you obstruct its view of the sky it will chew through batteries much more quickly. I am assuming you will turn the device off of a night in my estimates.
This is another really handy lightweight (50 gram) device for keeping in touch: http://www.theultralighthiker.com/gotenna/
As are these: http://www.theultralighthiker.com/emergency-cb-radios/
Update (Jun 2018):
Three is now a new half size Garmin Inreach weighing a mere 100 grams with all the same functionality: http://www.theultralighthiker.com/garmin-inreach-mini/
And there is a new improved version of the above phone, named the Atom which is waterproof and boasts a 16 meg camera: http://www.theultralighthiker.com/mighty-tiny-phone/
Things just keep getting better and better!
To see what else I carry in my pack see: http://www.theultralighthiker.com/a-gorilla-in-the-hand/