Well, if these type of devices becomes mainstream, cable phone will take a hit also. That's what I last had. But I haven't had landline service for 3 years now, having 2 cell phones in the home.
It was only Friday that I received this device, and it works good. But with old batteries, I can only talk about 5 minutes per phone. For those interested, here's a link to the device.
http://www.nettalk.com/
But I didn't buy from them, Wal-Mart sells the same device online, at the same price, with only 97 cent shipping to the home. Net Talk Duo charges around $11.00 for shipping. This savings almost paid for the set of batteries that I ordered for my phones.
It still has the 30 day guarantee, regardless of place of purchase. BTW, check out the energy savings over the current Magic Jack product. These are national averages, so these amounts may be more or less per customer.
http://www.nettalk.com/competition