Having the display background to flash, having caller-id displayed on screen,trigger strobes or dim audio on receiving call could be really interesting
we could probably have also conditions like, if this person calls and this presence sensor detected movement, transfer call to this number!
Both my office and home phones are IP based (SIP) hardware, on a hosted PBX. This is really cheap and could surely be optimized. In my case, I would register a SIP client as another extension and have it behave like any other phone. This way the signaling and all info would be available.
There is a project called PJSUA that could probably do all this from command line, but I am unsure if this project is still being updated or even alive...