Let's get the easy stuff out of the way. I developed a greasemonkey script for converting phone numbers to tel URIs in Firefox. Developed is a relative term since the work was pretty much done for me by some other folks who developed a similar script for skype. As many Skype users already know, one of the great things about these VoIP systems is the ability to integrate the phone into your desktop experience. Since I built this script, I have literally not dialed a phone number on my deskphone in over a month. It's all dialing from contact list, directory search, and click to call.
You can find the script here- http://userscripts.org/scripts/show/56262