The Lifeline will work almost anywhere in the world including Mexico, Thailand and the Caribbean. The design goal is to allow you to talk to your own diveboat if you have a problem. Or if you can't talk to them, you are able to talk to every other boat around you on Channel 16 (universal hail and distress around the world). Worst case that you can't establish voice comm's, you can press the red distress (DSC) button and your GPS coordinates and alert message will be sent to every modern radio around you ie. most radios built since 2002 and ALL radios sold since Feb 2009.
The thinking on this came from our own experiences running a liveaboard boat in the Gulf of Alaska and down at Socorro Island in Mexico. If a diver surfaces away from a dive site at Socorro, the only search and rescue resources are the diveboats in the area. There are no other boats or helicopters or such. So an EPIRB or satellite device is of no use - your distress signal would get beamed to a sat and then downloaded to RCC shoreside who would then try to task SAR resources. Except there are no resources at Socorro. Our thinking was why not defuse the situation right at the start and simply talk to your own boat or other dive boat in the area when you are still only 100 yards off site.
Hope this info is helpful
Mike