Yancey
At least in FAA land ELT's are required and have been as long as I can remember (
http://www.ntsb.gov/news/events/2012...ions/Smith.pdf)
They are activated (theoretically) by a G switch and/or cockpit remote switch (I don't recall seeing one in an airliner but I haven't spent much time up the pointy end of those). They don't (just like all normal radio) transmit from underwater even if it was activated.
Your link is as I say - it is required to have an ELT. That link does not specify "g activated" - just "fuselage mounted as far aft as possible" (to survive a crash). Older airliners have them "attached" in the aft cabin, and they are crew activated.
Yes - for FAA land (and some European) GA now seem to require 'g' ELTs, but I am not sure all airliners in service do?
Leading on, were the ac "interfered with" which seems to include Xpdr, ACARS, VHF etc. then I am sure ELTs were considered as well.