I use vonage for our fax line, everything else we just use cellular. I have used only cellular for years now. It is nice having one phone number and one point of contact. Leaves you with also just one voice mail to manage.

The only problem we have with voip is running our webcam out of the house, the fax machine doesnt like it to well when the webcam is running. We have to turn our webcam off in order to send and receive faxes. Sometimes that becomes a hassle. Other then that voip is the only way to go.