You can get an aircard from any of the major wireless carriers- unlimited will run you about $60/month from any of them. I have Sprint and I've been impressed with their coverage. Check with your current cellular provider- it's easier than starting new coverage with a different provider. I suggest anything but Nextel. We had Nextel and the wireless internet card was terribly slow. Switched to Sprint (this was during the whole Nextel/Sprint merger) and have been very happy.
As far as faxing goes, you have a number of
faxing options on the road. I don't use a broker- but I imagine it would be a good idea.
I fax from the truck all the time.
Also- you may want an all-in-one printer/scanner/fax/copy machine. You should be able to pick one up for a couple hundred bucks. They may be less now- we bought our current one about a year ago.