Just adding to the reports here. I've been using an unlocked Treo 650 in Portland, OR with T-Zones $5.99 since 2005. Earlier they had T-Zones restricted to web & email only, requiring use of a proxy. Could still tether through Bluetooth though, as long as the proxy was used. Occasionally they'd open it up completely, and then lock it down again. But a while back (year or more? can't recall) they opened all ports, ditched the proxy, and left it that way.
Got my N1 yesterday. Popped in my ancient SIM (got it in 2003 originally) and everything's running beautifully, 3G and all. My.tmobile.com still has no idea what phone I have when I log in.
I hope it stays this way for at least 9 months. Then I'll have made up the difference between the fully subsidized price and plan, and my current $43/mo plan and the $530 I paid. I guess there's not a way I could've gotten the $179 price anyway, since I'm already a T-Mobile customer. I'll make up the difference for the existing customer price even faster. After that, it's all gravy.
APN shows as epc.tmobile.com
PS- I am totally blown away by this phone handheld computer. The physical design is awesome. The display is fantastic, and the user experience is smooth. It's exactly what I wanted. I got my wife an iPhone for Christmas, and she likes it a lot. The Nexus One though, it's perfect for me as I love to tinker/customize and would've felt too restricted in Apple iLand. My only learning curve is the soft keyboard, but I'm starting to get the hang of it already.