Voip on VSAT

That's a pretty broad question. Predictably, the answer is "it depends." It depends on what quality you are willing to accept, what VoIP service you are using, what voice codec is being used, what bandwidth you have available, and how congested your shared VSAT service is.

If you are looking for Ma Bell quality using your regular phone with a VoIP service like Vonage or SunRocket, then you will likely be disappointed. It may work well when the VSAT network is lightly loaded, but when things get busy you can expect problems.

If you are willing to make a few compromises, then I suggest you try using Skype. You will be tied to your computer to make and receive calls, but it has a good chance of working because it is very bandwidth-efficient. You would not want to consider this as a replacement for your landline phone, but it will allow you to make cheap calls.