Is it possible to write plugins for the built-in contacts app?

My end goal would be to initiate a call by selecting a contact's phone number via the n8xx's contact app. The call would be initiated via Vonage's Click2Call "API" (https://secure.click2callu.com/), which is basically a couple of http get requests.

The advantage of using Click2Call is that I could use my IT to initiate a call to a contact using one of my POTs handsets instead of having to tie up my IT with the call.

I suppose as an alternative I could write an app that imports the ITs contact info but I would prefer a more integrated approach. Thanks!!