I have a VisorPhone which also serves as a modem. You need a dial-up account, and the phone comes with a pretty good browser called Blazer. The speed is only 9600 baud, though. I bought it primarily to use the phone, but I often log on to airline websites to get current flight and gate info. when I'm traveling.
The phone is only $49 if you sign up for a year of service, which runs about $70 per month for 600 minutes of nationwide (US) roaming.
I love it because it integrates beautifully with the Visor address book and I only have to carry around one nerd-pack instead of 2 or 3.
"In God we trust, everyone else bring data"