Just take the SIM out of your phone and stick in your BB. There should be nothing on the BB SIM worth saving other than the phone number you don't want. Once you have the phone SIM in the BB, you can go into the address book and copy the phone numbers from the SIM to the address book if you like.
But, I would think the hard part has to be done by your provider, cancelling the phone number associated with the BB and moving the phone number of the phone to the BB so you have a single plan and one bill. You might be able to just cancel the BB phone plan, but that would leave you with 2 seperate bills.
ps. stonent reply made no sense to me when I first read it, but now I see what he is saying. I think if you do your part like I said, and then to get the service combined, do what stonent said
But then as bad as Cingular CS can be, who know how they want to do it