The website indicated a 2 watt radio. If you have a good base antenna at each location, I could see an effective range of 8- 10 miles, give or take.
Don't forget, FM data causes ranges to shorten drastically, not because you can't hear a signal, but because the modem that is trying to decypher the 1's and 0's may not be able to correctly receive the entire packet of information. If one bit is missing, the data transmission is trash.
Edit: What I want to know is how they're able to use encryption protocols...