Juniper Research thinks the market for WiFi VOIP phones will be worth $70 Billion by 2012, but most of the phones will be WiFi/Cellular hybrids. And the WiFi-only phones will go the way of the dodo.
I'd always thought the WiFi/Skype phones would be a destructive force in the telecom world. But the lag introduced when using them to call land lines add microseconds build up between queries and responses. It's enough to make every call to feel like that one time you spoke dirty nothings into the phone to your girlfriend, who actually turned out to be your girlfriend's mom. At least, that's how it goes with Skype...and me.
So now, even in WiFi blanketed areas, it's just easier to keep my cellphone close by, and use up the free minutes I already have allocated.
Death Knell for Wi-Fi Phones? [PCWorld]