3. GPRS / SMS technology using a sim card arduino shield.
I have tested many cell models myself flying, and they do not reliably reach a site 50 miles away. If they do not reach any site, then certainly they cannot interfere with one.
For heat, throw in a couple of those cheap iron-air hand warmers.
Transmitters:I'm using xbee pro transmitters for prototyping (putting the payload on RC airplanes, etc.) and there is a high powwer, pin compatable transmitter with a 40 mile range that I'm considering for the payload.
My wifi network did not "connect" with my cordless phone, but every time someone talked on the phone my wifi network would stop working.
Most mobile phones can receive a signal much further away then they can transmit. It's easy to prove this
At altitude, no air == no heat.
No air also means no buoyancy, ie: a balloon cannot get there.
They will generate some heat wherever this is some O2, and buddy's balloon is not going to exit the atmosphere.