Forum OpenACS Q&A: Export and import contacts between webmail apps

I've been studying how to export and import user's contacts from one webmail client to another with user's authorization.
I could get good results only with google APIs.
All the rest, it seems they hide the ways or make it hard to get those info. Or only provides a records.

Furthermore, I found several companies/websites that have this expertise pretty much standardized on the webservices.
Such as:
TrueSwitch - http://www.trueswitch.com/
Openinviter - http://openinviter.com/
IPInvite - iplusmedia.com/software/
Facebook -

Does anyone know these companies/websites easily export and import email contacts from one webmail account to another?

Best wishes,