FWIW I think a key issue that might be important to consider for those who are safety concious is that unless your VOIP provider (like Vonage) provides electronic 911 services, if you go with any basic VOIP provider like Skype, for example, you may have to forgo 911 service. Skype is very clear about this. Plus you have to sign up for two services with Skype (Skype in - which includes an incoming telephone number, and Skype-out). Skype is great, but it is not a multi-phone solution as Fred mentioned in the other thread.
I don't know anything about "Jack" and 911, but it is worth investigating. I have used Vonage for 4 years and been very satisfied. I will never go back to a regular line if I can avoid it. Also, if you call and ask Vonage allows you to pre-pay for the year and get two months essentially free as an incentive.
For those DSL only folks - don't forget that you don't HAVE to sign up for a regular POTS line to get DSL now that "
dry or "naked"-DSL" is also an option in some areas (although it is often more expensive).