Can I sue another Realtor for stealing my leads (sign calls), because when you call my business line and press 0 for opertor, the calls are mysteriously forwarded to his cell phone number.

First how is he forwarding the calls, ( you have to prove he did it) Is he another agent in the same office ? Are you both agents or both brokers ?

Assuming that he did it, then you would also have to prove, with respect to each commission he earned, if it resulted from a transfer from a call that would have gone to you (as opposed to someone else). Possible, but I can see it being complex.