they had something like this out earlier this year for blackberry. it would be nice but from what I recall reading you had to have at least 1 radio capable of hooking up via ip to rebroadcast to the units. I am also aware of an op called voxer that is similiar to PTT, my son was playing around with it some time ago and you can send private, unit to unit, group calls, voice, text photos and it will even send your location. would I trust this in a public safety type arena, probably not, but then again I am old school and working NY we were required to have at least 2 types of communication on the rig. most was done via nextel or 2 way. I'll tell you this also if you had to patch by radio to the ER (155.340 or 155.355 if I remember - I left in 2002) and were anywhere near the tappan zee bridge, you were screwed. there was a volly corps that used the same freq and their repeter would blow you right off the air.