I am not 100% sure, but there might be a way, it would have to be a Controlled API call because of the security implications: http://www.blackberry.com/developers...lledAPIs.shtml
Purchasing a key costs $100 USD, to gain access to these 'priveleged' API calls.
RIM protects the more 'dangerous' API calls with a cryptographic signing key to prevent it from being easy to hack BlackBerries compared to other devices. For example, a virus automatically making a phone call is not possible without getting a cryptographic signing key to give you (as a programmer) permission to write such software. This is because RIM's major customers are governments who want secure devices.
If you are looking to write a program that has an auto-answer, and it is not listed as a Controlled API, you may wish to contact RIM directly. It may be an undocumented API call.
There are supposedly more Controlled API calls becoming available with BlackBerryOS 4.0 which will prove useful to programmers. So it may be possible. I know that OS 4.0 is supposed to allow applications to make phone calls -- probably a Controlled API call that requires the special key.
Note: No, I don't know what other new Controlled API's exist in OS 4.0 ....