I use the Phono SDK from Voxeo to enable phone calls from a web page on a couple of projects which include the Inspired-Social (WordPress/BuddyPress) plugin for Openfire. I like using Phono SDK, but it is dependent on external cloud servers in the Internet that cannot be accessed in some situations.
Recently on request, I had to modify it to work directly with an in-house Openfire server to provide Jingle voice calls over the RTMP and RTMFP transport as well as SIP calls to PBX phones. The result of that work is now available as Redfire-Phono which replaces the Red5Phone softphone in the Redfire plugin for Openfire.
For more information about Redfire-Phono, see the latest release note for Redfire