Wireless carriers in the US have a great habit of stating the term "unlimited" in marketing materials only to renege on that message later on. T-Mobile USA's reference to an "T-MobileWeb unlimited for $5.99" would make one think that accessing the web from a T-Mobile phone would be $5.99 (per month) for unlimited usage. The devil is in the details here: as some T-Mo customers are finding out, "unlimited" from the T-Mobile dictionary means regular handsets only using data connections through port 9021. So, are PDA phones and other smartphones left out in the cold here? From all appearances, yes. Those devices generally use port 80 (or 8080), which is blocked for T-Mobile customers subscribing to the $5.99 T-MobileWeb plan. Want more "unlimited" data on that T-Mobile Dash? Better be prepared to shell out $29.99 for that kind of "unlimited" service, unless you want to use T-Mobile's proxy server for everything.
Update: It seems this bizarre on-again, off-again practice of T-Mobile's has been going on for some time and continues to this very day -- some folks are having luck bypassing the proxy, others aren't. Can we please get a uniform, official policy here?