VoIP on Vsat

All shared access VSAT systems with time division multiple access (TDMA) uplinks systems are primarily suitable for intermittent internet browsing and emails, where you only occasionally transmit a brief burst.  To make such systems suitable for VoIP, which requres a steady stream of packets in both directions, requires that the system be configured unusually.  Your transmit uplink bursts need to be given regular priority allocated time slots so that your uplink bursts form an uninterrupted steady stream.   

As you have found, the cheapest mass-market service providers are not suitable for VoIP (or any other heavy demand uplink applications- audio/video streaming etc).

Systems like Hughes HX and iDirect can be configured to provide good VoIP but this needs skill to set up.  You must also configure your phones for appropriate speech coding and speech samples per packet.  This is all rather complicated and you may need to cooperate for some time on a technical level with the VSAT hub to eventually get a working system.  VoIP service providers/VoIP gateways may be different companies and this complicates issues further.

If anyone can offer VoIP service via satellite in Scotland, please say here.

My VoIP experience is with dedicated SCPC transmission, e.g. 12kbit/s up and down, providing one perfect VoIP call 24/7, such as for a remote phone booth/cafe.  Such dedicated capacity is rather expensive (e.g. $168 per month) if you only make a few calls per day.

Have you considered using a terrestrial radio link ?

Best regards, Eric.