There is a free VoIP service that is a web-driven SIP phone
With that service you can use your favorite SIP community / provider settings to make VoIP calls directly from the web page.
Address:
http://www.doddle.com.br/endoddle.jsp
it is a kind of click2call:
You can create a web phone HTML link to call directly from the webpage, for instance, a bookmark: (substitute parameters with those of your VoIP provider values):
HTML code example:
Or let other users to call you from web: