From the TMobile site it looks like they do offer BB Data for $10 a month, but only with $50 monthly 4g plans, NOT prepaid, pay by the day or pay as you go plans. Look here
. Includes access to BlackBerry email, BlackBerry Messenger, and BlackBerry App World for your BlackBerry device, for an additional $10 per month.
For Monthly4G plans $50 and up. Not available for Prepaid - Pay by the Day and Pay As You Go plans.