Display custom text in-call

[lukeescude]

It would be really awesome if we could send a custom SIP header in the INVITE with some custom text to display to the user (for inbound calls).

If we send an INVITE to the phone with X-Awesome-Feature: Hello! it would display the string "Hello!" on the screen, beneath the call info.

This opens the doors to lots of cool functionality, like adding spam ratings to inbound phone calls.