Basically, not a chance. Blackberries have a PIN. That PIN only works from Blackberry->BIS servers->Blackberry. In other words, it requires the use of RIM servers. BBM uses the PIN to communicate. The only way ways to get this to work are:
1) either get RIM to let others use their servers, of course you'll need your own PIN (good luck getting that)
2) buy a Blackberry with a BIS plan, write software for the Blackberry that routes BBM through it (ie. create a server app that runs on the Blackberry and allows you to connect to it using your Nokia, the app then needs to forward your messages to BBM and vise versa) - you might as well just carry around a Blackberry.