RF used in recreational scuba now?

Hi folks,

I did the PADI certification thing (up to "Advanced Open Water") about ten
years ago, but unfortunely never did a whole lot of diving afterwards.
Well, this summer, I'm planning on getting back into it. Just bought a
tank and have my eyes set on a new BCD. Plus, of course, even though I
still am familiar with the stuff that is the most important (using tables,
pressure groups, safety stops, etc), I'll be taking a refresher classes at
a local dive shop as well.

Anyway, all that is pretty much straight-forward.

My question is more of a curiosity.

A short while ago, "Discovery HD Theater" was airing one of those "watch us
dive with the sharks"-type show. I don't remember the name of the show,
but like all the other nature shows on "Discovery HD Theater", it was
pretty cool to just vedge out on the couch and watch the clarity/beauty.

What was interesting:

The divers on the show were wearing just your standard open water type gear;
facemask, snorkel, fins, BCD, regulator, etc --- but they were
communicating (audio) to one another, electronically, with (literally) no
strings attached. They were even communicating with one another with quite
a bit of distance of separation between them. At one point, one guy was
even well inside a cave, while the other was outside (and above). The
audio was real-time and wasn't dubbed in for the show during editing.

So, the question here, is obvious; How and with what?

Are (underwater!) RF communication systems now withen the realm of
recreational diving?

Just more of a curiosity than anything else. Actually, I don't even think
I'd want to use audio during dives, anyway, as it would kind of kill the
peaceful tranquility nature of it all.

It seems GPS could be very useful though -- without having to tow an antenna
like a 1/4 mile long!

Thanks,
Eric