Data speed?

Hi -

I'm finally contemplating of updating my phone. I would like to stay with my old plan which tmobile has labeled as 'unlimited blackberry' plan. (Unlimited calls and data). My current phone is Blackberry Pearl so at the moment I'm not really taking advantage of the data (except for reading my emails).
If I get a new unlocked or tmobile 4G phone (Android or Windows) from ebay, can I just put my sim card in the new phone? What would be my data speed? Would it be 4G or something else?

Thanks!

It depends on what phone you get (HTC Amaze 4G is highly recommended, HSPA+ 42). However, they might want to change your plan and may just do it automatically w/o you knowing.

If I get a new unlocked or tmobile 4G phone (Android or Windows) from ebay, can I just put my sim card in the new phone?

Sometimes Android phones will not work on a blackberry plan.  You may need them to provision it to an Android plan if it doesn't work. 

If it does work, your data speed will be as fast as the device will do.  There's not a special 4G data plan needed.