According to ZDNet:
Forrester surveyed 1,132 online US households to gauge their awareness and interest in services based on VOIP technology. 43% of our respondents had heard of VoIP before taking the survey, with word of mouth as the biggest driver of awareness at 23%. But awareness did not translate into sales because a mere 3% are using a paid VoIP service and 1% are using a free service. Only 13% are interested or very interested. With somewhat interested users, the total barely breaks 36%. When asked why they aren't interested in VoIP, more than 60% of consumers said that they are satisfied with their existing service. 50% also feel their services are reasonably priced.
My view is these numbers will change over time as VoIP becomes better known and broadband becomes more widely available. AOL launching VoIP in the next 30 days for their broadband five million subscribers will have an impact.