Many thanks for the reply.
Is ISRv free for home use? This is for 4/5 phones max so I don't want to be paying too much if I can help it.
Not sure about the features, a friend set it up. I think it's running Advanced Enterprise Services.
There is no VPN. The router and phones are in my house on the same network. The router is on it's own subnet and is only for the phones.
I was hoping to use a small low-powered PC for the virtual image.