CellFrog just announce their syncing capabilities with your google accounts.  I just tried it out and it worked seamlessly.  Originally when CellFrog was first made public they had Plaxo syncing capabilities from the start.  The thing was that all of my contacts were in google, so manually entering all of my contacts to make a conference call possible was quite a task.  But as you can see in this screenshot, all of my contacts have been added with just a simple connect Google button.

Going beyond your contacts they also give you the ability to collaborate using Google Docs through their system.  Checkout the screencast below and view how quick and easy it is to integrate.