Prior Art
Isn't this was DeskSMS does already?
Phonedeck's promises to integrate an Android phone with a desktop computer though PIM synchronisation could yet prove its downfall. The service launches today, with an Android application and an HTML5 control panel. The application enables the control panel to make and answer calls (on the mobile) as well as manage SMS …
"The problem is that, in the UK at least, most of us reach for a desk phone when making a call"
The thing is that this is demonstrably false. People have their contacts on their mobile, and that's where they dial from (except for possibly conference calls where the number is in the Outlook invite). This seems to be taking single point of presence functionality that's getting big in the corporate world and giving it to the regular end user, which for free isn't bad.