They also have another "feature" that works the exact same way when you sign-up with an e-mail address that someone had in their address book and used the "Impo

They also have another "feature" that works the exact same way when you sign-up with an e-mail address that someone had in their address book and used the "Import contacts from feature". You can try this with a fresh account. I'll be writing a blog post about it, as well, soon.