Leadstream,
Alright, I looked at the Phone Manager 4.2 guide and the only way that it changes the CPN [Calling Party Number] is via the Agent Hot Desking feature. In reality it just uses the CPN of the Phantom port created for the agent and doesn't allow for it to be changed on the fly.
As for the API you will need to contact someone at Mitel Solutions Alliance about what can be changed via the OAI stream. Prior to OAI v10 this was not a feature, but then again neither was CPN and I have no experience with the API after v10 came out; sorry not very many customers want to create and support their own applications. If I had to make a guess though I would say that it is possible since the CPN does show up in the OAI stream.
Thanks,
TE