I design PBX networks and have a VoIP lab for evaluation of VoIP for my company.
I use to setup video conferences and backup PBX links using Satellites. I have not done any VoIP over Satellites but the equipment was a T1 (digital tie trunks) from the PBX to a echo cancellor and then to a MUX and then a Satellite modem that was limited to about 768Kbps. The MUX was a propriatary 8Kbps packets with silent suppression. We sustained delays of over 160ms which people do not like. I belive VoIP will be similar. The Router will simply take the place of the MUX. IP will add more delay – at least 40ms more.
I have 6 Cisco 7960 IP Phones in The Netherland Antillies over Satellite and then public IP to Atlanta without a problem. The ping is 500ms but sounds better than a PSTN call and has American dial tone.