This is pretty much the coolest thing in the world! I am posting from my laptop which is connected to my cell phone's wifi connection, using Sprint's EVDO connection to the internet. The software that enables me to do this is called wmwifirouter. Earlier this month they released their first final version of the software, and started charging for it. It's not outrageously priced, but you can still find the earlier free versions on the internet if you search for versions 0.90 or 0.89.
Well I did it! I got the HTC Mogul on Sprint's SERO plan. Everything has been pretty painless so far. Activation was easy, text messaging works, and Internet browsing is pretty fast! Now comes the hard part: getting my data to sync between Windows Mobile and OS X.