MrsFrog and I have two little motorola two-way radios, only £30 odd, very useful at shows and on the road (although probably not legal as they are not hands free).
Approx. 3 mile range apparently

No privacy as said above, at the devon RS show, someone asked over the radio if I wanted a drink, so I replied saying yes please, coffee.... I thought I was talking to spiky.

It was a complete stranger though

Then spiky took the radio and started telling all he was the only gay in the village

They are cool, and would certainly help with mobile phone costs.