I don't believe T-Mobile supports having two SIM's actice simultaniously for the same for the same number. There are ways to clone SIM cards but that us something I wouldn't recommend doing. T-Mobile would be able to detect duplicate SIM cards on their network and it would more than likely trigger a security/fraud alert for your service.
Currently only available with iOS and Android.
I think BB10 may have had some early access during Digits beta, but I think that was using a workaround through a web browser. BB7....I'm going to say no.
Of course you can use the iPhone with 2 numbers on a digits talk and text plan. But I think the BB is a no go.
So we do have a Data with Paired DIGITS plan for Business lines that would give you a duplicate SIM for that Blackberry and we also have a BB internet feature that would give you BIS for that line. Please call us when you have a moment so we can take a closer look at your account to see if you qualify.