err... I took the languages list from a wikipedia page, not sure if it includes ALL the obscure languages but I saw something about phoenician, so I'm going to assume we have most of them covered. Problem is finding two people that are interested in said obscure language.
I believe the OP was suggesting that two people could use the service as an alternative to Skype if the two parties picked a very rare language such that the odds are that they would be the only two.