proxy for voip

I have had some difficulties with using voip through an openvpn connection. The vpn connection sometimes gets dropped. This has resulted in people not being able to reach me, and I have missed very important calls. I must be able to have my voip softphone active and waiting for calls all the time. My softphone supports proxy servers, so I would like to find a RELIABLE proxy service that will not drop me and run my voip traffic through it. Does anybody know a proxy service that would be appropriate for that?