In-Stat asked around and apparently found not much interest:
Wi-Fi-only phones could theoretically replace cellular phones for some users, but respondents that participated in an In-Stat Web survey around Wi-Fi phones and communication devices had only a lukewarm response to the concept. Although the majority of respondents expressed at least marginal interest in Wi-Fi-only phones, nearly 25 percent expressed absolutely no interest, the high-tech market research firm says.
One inhibitor the firm found was price. “Current pricing for Wi-Fi-only phones is way out of line with what most consumers are willing to pay,” the firm noted. Survey respondents were also happy with their cellphones.
Consumers were interested in paying more for a Wi-Fi-enabled “personal communication device such as the Sony mylo” vs. a standard Wi-Fi phone.
Currently, EarthLink is trialing a Wi-Fi telephone service in California.