Sorry I was just thinking about non-video conferance uses. If you have something as small as an iPhone and can get a live recoding camera on both ends you can theoretcally record in stereo, which is needed for 3D. Just pointing out that with the current iPhone at least an add-on cam would create a spacing just a little wider the normal human eye placement.
As to conferancing, that's simple. Just snap on whatever exteranal cam they create, launch the App, and hopefully let the iPhoneOS handle the rest.
On the 3D side shouldn't the iPad have a fast enough refresh/redisplay rate to allow for stutter glasses. LED can't do polarized, but with Bluetooth stutter glasses should be just fine. (one eye opaques, then the other, at rate and in time to frames, to trick your brain into seeing stereo.)