Is there a webservice or API to help me read email contacts?

I am trying to add a feature in my website to let the user invite his email contacts to visit the website, the same as twitter and facebook are doing.
I got bored from trying to implement this feature for each email service, for gmail, yahoo, msn. and when I success in implementing one another one change somethings in their APIs and i start to debug the problem.

By the way, is there an API or a webservice I can use which can give me this feature?

enter image description here

What is an API for email?

What is an Email API? An email API allows applications to access functions offered by the email service provider's platform, including generating and sending transactional emails, manipulating templates, moving or editing folders, building drafts, and more.

Found this API http://code.google.com/p/socialauth-net/ and seams good, will test it and write here later the result.