http://mobilitytoday.com/news/006573/ballon_cell_tower

Building a conventional cell tower can be problematic for a couple of reasons.

Cell towers are expensive, costing from $100,000 to more than $1 million to set up. They also present logistical problems, such as clearing local regulations and finding suitable placement.

Space Data uses standard weather balloons, which cost about $50 each, to carry special purpose cell towers. These towers are small -- 10 cubic inches -- and light -- less than 12 pounds. The balloons travel 20 miles above the earth, well above commercial airliner pathways. Because of their highflying position, the devices cover a larger area -- from 50 miles to 500 miles -- than traditional cell towers.
I have recovered a weather baloon and transmitter ... it broke a windshield on my neighbors car when I was about 15 due to its paper mache parachute failing and it "rocketing" to earth....I remember it weighed about 6 pounds when mailing it back to NWS....12 pounds , now that could hurt !