If we continue to be happy with it, we'll be dumping AT&T in favor of a lifetime of free (or cheap, if we continue with the Premier Services) phone service. We currently spend $36.95 per month for a single phone line + Caller ID and Call Waiting. All that comes free with Ooma for the initial outlay of $200. In other words, it pays for itself in less than six months. Six months! If we stick with Premier, it means we save $343 per year (assuming rates change on neither side).
The only other equipment I'm going to add to the mix is an uninterruptible power supply to insure we have phone service when the power goes out.