PHP InviterPlus is a very complete PHP contactimporter. It does not only import contacts from all major email providers, but it also imports you contacts from all major social networks like Facebook.
Furthermore, PHP InviterPlus has the ability to directly send the invites to the contacts you select, even if they are contacts from a social network.

The scripts and classes of PHP InviterPlus is easy to implement in your project.
Some of the providers that PHP InviterPlus supports:
- Gmail contacts
- Hotmail Contacts
- Windows Live Contacts
- Yahoo Contacts
- Facebook
- MySpace
- and many many more

This is the most complete php contact importer out there. Go ahead and give it a try.