BIS and OWA do work and play together. I'm on TMO and have had my work email (MS Exchange 2007) for about 2 months now.
But Penguin3107 is right, RIM hasn't "blessed" it yet.
Go to the TMO BIS website (log into your My T-Mobile.com) and add the account.
If you give your email and password it should work. It might ask for more settings (domain, user name and url -
Https://etc.).