You can build your own:
http://www.stompboxnetworks.com/

Or you can buy one now:
http://www.google.com/products?hl=en...num=1&ct=title

3G to WiFi has been around for a while now. We were running Cisco Aeronet routers that had a 3G PCMCIA card in one slot and a 802.11g card in the other while I was at my last job Since then, we've been pouring our resources into Buffalo routers and XOHM WiMAX.