I've had VOIP for 4 years and not had many problems. I think simultaneous ring was one reason for this. Although I've had more problems with VOIPO set up than with any of the other providers I have been with, their customer support is first rate and the quality of their phone calls are superb as well. As long as the provider has a fail over number system in case of a power outage (which VOIPO has) I think think/hope these glitches will get worked out. At least I'm willing to give them the benefit of the doubt for a short while.
And yes, they do have my cell number, but can't seem to remember that I now have a separate cell number. It's no longer one number reaches me everywhere!