Outbound "silent alarm" call

[mercutioviz]

I have a user who is investigating a possible usage for his Yealink phones. I suppose it could best be described as a "silent reverse intercom" call. The idea is that a user could press a button and the phone would go into speaker phone mode and dial out, however it would not emit any sound - no ringback tone, no audio from the person at the other end. However, the person on the other end would be able to hear what's happening at the caller's end.

Setting aside whether this is a valid feature request, I am interested in the technical aspect of this challenge. Is it possible to make the phone do something like this, perhaps with XML browser functionality?

Thanks,
Michael