I have found a way to create a wireless network in our motorhome, using a linksys wireless router and a ATT 3-G air card.
I am using a ATT 881 G-3 air card and a Linksys model #WRT54G3G-AT. This is very effective. We have service going down the road. I also installed a Wilson truckers cell antenna with a Wilson PCS824-894/1850-1990mhz amplifier that transmits a signal inside of your coach. We have mostly 5 bars from that unit. This allows both me and my wife to use the internet at the same time. She has a Apple and I use a Dell. Hope this helps. Also ATT does not support this use.
Dale & Molly Hannon