Pingplotter will, hopefully tell you were the problem is occuring. If, for example, you are getting timeouts at the phone system IP card, but the hop just before that one is looking good, then you have to look closer to that side. If the gateway to the phone system looks good all the time, thing maybe something internal, like a data switch, or the IP card itself.
If the problem is somewhere towards the middle, then it is definately a problem with the internet connection. Not sure how to solve that one, except to try calling the provider and seeing if they can help.
You are seeing ping results from the connections on the way to the phone system. Rememeber you are looking for where the connection problems start.
In order to create a VPN for the phone system, you would need a router on each end to create a tunnel, which means you would have to put the IPU on the phone system behind a router, then everyone that connect to it would need to use a VPN.
