Calling facility in My Website

We are developing a Social Networking Website (www.numbertank.com), and we would like to give calling facility over worldwide within our User's Profile Page on submitting the 'calling button'.  If you have any API, SDK or any other source, let us inform with full detail of Hardware requirement, Operating System and Calling charges/subscription/monthly plan etc.   Or give the Contact No. of your technical person who can talk with us regarding mentioned subject. (this will be better for us to communicate) With Regards  - Manish Sapkal
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