Sony Ericsson S710a

hi i just purchased this unlocked s710a and i absolutely love the phone. i have a tmobile Sim card and the 5.99 unlimited wap browsing but it won't let me connect to the "Media net". it starts off by showing "connecting" then "loading" and the little globe shows on the top and then all of a sudden it shows "connection failure. contact service provider." i also tried to send the settings to the phone via the website but still samething. ANY HELP WOULD BE APPRECIATED!! thanks