I have a few more details to provide on the DeLorme Earthmate PN-60w and SPOT Satellite Communicator introduced at the Consumer Electronics Show in Las Vegas. However, it is just a few more details because from my discussions with SPOT it is clear that a lot of the specifications and such are still not finalized. So what more do we know? See here:
http://www.equipped.org/blog/?p=207

802.15.4. Hmm.

Interesting - zigbee has an uiltralow power sleep mode over Bluetooth.
It might be possible to make the spot puck so it doesn't need an on/off switch, you could leave it sleeping until the GPS sends a message. That would certainly be safer in an emergency.