I recently signed up for BIS through T-Mobile
It is set up through OWA, an exchange server. I have a Blackberry Curve 8320
I would like to know is there an easy to to retrieve previous emails prior to my signup?

I have using microsoft outlook to mark the mails as new, then go into the mailbox on my BB and "reconcile now", but no luck.

can anybody help?

Not if your on BIS, can only be done on BES.