I'm not sure what you mean by an EPIRB. I typically carry a VHF radio in an otter box but have found it obsolete in some areas and not used in others. So I too am rethinking the strategy. I guess a cell phone with built in GPS would be the way to go inside of an otter box.
Komodo NP isn't a great location for cell phone signals except when you are very close to Labuanbajo (and even then...). This is also true of some other great locations for diving in Indonesia (Raja Empat, Banda Sea, and Wakatobi National Park), and I think the situation is probably similar (still) in PNG.
VHF only works for line-of-sight communications, which can be problematic in areas with lots of islands, such as Komodo and Raja Empat. A waterproof mobile VHF would obviously be useful if you were adrift and could see the search-and-rescue (SAR) vessels, assuming that they also were equipped with a VHF radio, but one cannot assume that all craft participating in SAR operations in locations like this would be equipped with even VHF radios. It would be even more unrealistic to assume that vessels participating in SAR operations in Indonesia or PNG would be equipped to monitor the 406 MHz distress signal from an EPIRB or PLB or to pick up the 121.5 MHz homing beacon.
Of course, if you are within sight of a rescue boats or planes, then the rescuers should also be able to see you, provided that you have a large-enough submersible marker buoy or sausage (if it's still daylight), or a good light or emergency flashing strobe at night.
The fundamental emergency kit which anyone diving offshore should have, particularly in locations like Indonesia's Komodo National Park, remains the same: a large SMB or sausage (ideally 2 m or bigger.), a good light reserved for emergency use, and a powerful whistle. Adding a flashing emergency strobe, an inflator-hose-powered horn, a small mirror, and a couple of dye packs won't hurt. All this can also be easily carried or incorporated onto any BC.
After that, it might be worthwhile also considering adding electronic communication devices such as cell phones or EPIRBS, but one should not rely on these devices being effective in every location.
Robert Delfs