Thanks for your replies.
So, in theory it is possible to use VOIP over a satellite connection if we don’t mind the latency delai.
The 2way satellite providers I contacted in France all said no VOIP can be effectively used on their channels.
But now I start to think it is more an excuse to limit the quantity of data transmission as satellite channels are share with other users.
I think I will go for a 128k/512k satellite internet connection as the monthly rental is about the same as an unlimited ISDN, with the distinct advantage to allow shared use with neighbours over a Mesh Network for example.
Thanks for the info on the Quintum’s.