|This is a really open-ended question you can't hope to have answered decently.|
I don't use VoIP at home. We do however use VoIP where I work. But we have a controller between our VoIP and our PBX which acts as the interface between the two systems. You're asking about (I think) public VoIP systems of which I have no experience........or interest in trying at this point in time.
If you're talking about public VoIP systems then you'd really do better to research each on your own and look for, and read through, other peoples reviews of each system/provider.
At best, all you're going to get here is the very same thing, personal opinions based on personal experience, and I wager you won't get 3 of those here. So get off your butt, get googling and start your reading and research.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.