German-based Nova Media landed on our radar last year with their iSync plugin that supports more phones than Mac OS X's default set. Not content with mere syncing, however, the company also makes an Address Book plugin, recently updated with more supported models, that allows phones from Nokia and Sony Ericsson to shake hands with Apple's contact manager for all sorts of phone call integration. Sending calls to voicemail, replying via an SMS, logging the call and even starting one are all possible from within Address Book. And while AB supports these operations with the default batch of iSync-supported phones, Nova Media's Address Book plugin enables these operations with a large set of Nokia and Sony Ericsson phones that Apple likely never will support.
Unfortunately, there doesn't appear to be a demo available for download, but at roughly $8.50 USD (Euro 6,50), I bet it would be hard to go wrong. After all, I can say from personal experience that $8.50 would be a small price to pay for the satisfying ability of clicking a button in a Mac OS X dialog to send someone directly to voicemail.