People will frequently encounter phone numbers in their web browser. They may be browsing an arbitrary web site or they may be accessing a business application that doesn't have any native click to dial support.

Web application developers can markup phone numbers as hyperlinks using the tel: URI prefix. This makes the phone number clickable just like a link to another web site or an email address. Unfortunately, few web developers have taken advantage of this feature.

The Firefox plugin Telify solves this problem. It scans the page you are looking at and dynamically converts phone numbers into links that can be clicked.

Many people use a productivity suite like Mozilla Thunderbird or GNOME Evolution for email and address book purposes.

For Thunderbird users, the TBDialOut plugin makes phone numbers in the address book clickable as tel or sip URIs. Dialing is then delegated to the URI handler on the user's system.

For Evolution users, using v3.13.2, there is support for clicking phone numbers and SIP addresses that have been added to the address book. Evolution will only make them clickable if it detects that a URI handler is installed.

A simple way to handle the tel and sip URIs is to install the sipdialer from reSIProcate. The sipdialer utility can send a SIP REFER to various SIP phones that support this mechanism, including Cisco and Polycom. It is available as a package on Debian, Ubuntu and Fedora.

There are various scripts available that can send an instruction over HTTP to an Asterisk or FreeSWITCH server to initiate a phone call. One of these scripts can be installed as a URI handler for tel and possibly sip URIs on each user's computer.