After endlessly searching for a way to use my phone as a modem without working through Verizon, I came across USB Modem, which not only allows you to use the Treo as a modem, but also utilizes the faster USB connection. Only the Treo 700p offers speedy broadband access; reportedly 10x faster than dial-up; I don't know how fast pages load with the 600 or 650. And BTW, it syncs flawlessly with Apple's Palm iSync conduit.
[robg adds: I haven't tested this software, and note that it's $24.95 -- however, there is a demo version you can test to make sure it works for you prior to purchasing. Please keep in mind that you are responsible for anything you do to your phone, and/or anything that your service provider may then do as a follow-up to your actions.]

