tethering imac

I have a unique situation. I would like to tether my imac to some sort of smart phone and share services. I also have a need to take this setup on the road in my motorhome. Home is in a fair signal area .and on the road I will be seeing a wide range of signal strenght and would like the option of adding an external antennaI have a newer 24" imac running snow leopard with an airport express. I am open to usefull suggestions. My first choice would be to tether iphone but don't feel up to the apparent hassle it takes to do it. The local phone stores are no help. Ideas??