I agree with Nil on Vonage. I have had a Vonage number since moving to Switzerland from the US, and I have been highly satisfied with it.
In order to obtain the Vonage phone, I simply called Vonage (info at
www.vonage.com) when I would have normally called the local landline phone company to arrange for line disconnection when I moved out of my home in the US. I was able to keep my old landline number. I paid for the equipment from Vonage, received it via mail, and all was set. I would encourage you to make sure your bandwidth speed is high enough in order to assure quality performance.
The only downside is the occasional call from a local or state politician during elections season, which usually comes in around midnight or 1 a.m. here in Switzerland.
Incidentally, you can also have a pretty good time telling a US sales caller that you are interested in carpet cleaning or an alarm system, giving them a four-digit postal code and seeing what they say.