The "web2go" plan is designed to provide internet for "non-smartphones". Would make sense if a proxy is compressing images/sites to speed up browsing on the underpowered devices. I had the $10 web2go plan for my unlocked Nokia n900. It worked, using the internet2.tmobile.com APN. However speedtest.net results always had me with really high latency, and showed my location as somewhere in the midwest, when I'm near DC. When I was put on the smartphone plan ($25), following a call to tech support, they told me that I should be on epc.tmobile.com APN, and that "everyone" should be on it. However, that APN did not work when I was on the web2go.
While my ping times went down, and my new gateway/proxy were geographically closer to me under the $25 plan, I switched my plan back to the $10 online. When the change took effect at the start of the next billing cycle, when trying to access the web, I was prompted to "upgrade my plan" and that "the web service is not designed for your phone" messages.
FWIW, I was still getting over 4Mbs under the $10 plan. There also may have been a change which allows the web2go plan to access the web via all the APNs. What does that all mean? It means that an unlocked "super phone" should be able to use the $10 plan without issue, and still experience the 7Mbs+ connection.