callto
Callto is a URI scheme used by some voice over IP (VoIP) applications to initiate a call to a specified contact. A link that uses the scheme, such as callto:username or callto:+15551234567, is intended to launch the associated application and begin a call to the indicated contact if the application is installed on the system.
Origin and usage of the callto scheme are tied to early VoIP integrations, most notably with Skype.
Syntax and behavior are generally straightforward but vary by implementation. The basic form is callto:<identifier>, where
Compatibility and status: Because callto is not a universal standard, support is inconsistent across browsers, operating