It's not free, ($5.99/mo) but I use iPlum to maintain our old US phone number after moving in Europe. If you ever plan on her business growing, you might consider a solution that will grow with you: iPlum can support multiple numbers on an account, and even an IVR/menuing system. I picked iPlum because it's one of the few VOIP services that allowed me to transfer in a number--which also means you can transfer out. They even have toll free numbers available, if you went big time.