If you want to add a call me button to your own page, here doddlephone can help you, all you need is to have a sip account that can make outgoing calls to PSTN (phone numbers)
Here is how:
<iframe src="http://widget.doddlephone.com/embed/webphone.jsp?sipserver=yourSIPserver&username=yourUsername&password=yourPassword&callto=PhoneNumber2Call&label1=Call%&label2=Hangup%&mode=button"
frameborder="0" width="550" height="160" scrolling="no" ></iframe>