Do you mind sharing the details of your proxy settings? Which APN are you using hiptop.t-mobile.com, epc.tmobile.com, or something else entirely? I've tried many permutations with this same plan in the last couple of days and I've not been able to get anything besides a re-direction to "t-zones." Any tips would be greatly appreciated (I have certainly tested multiple proxies and ports 25, 993, 995, etc). T-Mobile sales reps told me that the their "data prepaid plan" (the sidekick plan) was compatible with all smart phones, but once I put $100 dollars on it (and learned that I cannot go back on a prepaid plan) - I learned that their official word is that only the sidekick works with the sidekick data plan.

P.S. If you're running your own proxy or something, then please PM me if you're willing to let me try it out.