You need to have broadband cellular service in your area. If so, then you buy a wireless card from your cell company and get a data contract- about $55/month or so if I recall- and you can get pretty good speeds with that. If your cell company only has older technology, they'll still happily charge you up the butt for a wireless card, but the speeds won't be any faster than dialup.
I have a cable modem, but I have a Treo 700p that I tether to my laptop via bluetooth and I can get 3mbps speeds through that which is pretty awesome
Another option you have is a satellite modem.
[This message has been edited by SteveFehr (edited 02-02-2007).]