Nokia 6101 and T-mobile

I've recently acquired an unlocked Nokia 6101, formerly on T-Mobile in
the US. It works well - except for the fact that I can't change the
T-zones settings. I've downloaded the settings for MMS, and the phone
accepted them. WAP and internet settings appear to download, but only
t-zones appears in the list.
Would flashing the phone fix this? And if so - how much is it likely to
cost?