Dont bother with VOIP service. I've tried with countless ones, either too expensive for the quality or plain just sucks. I bought a magic jack and im not sure how i lived without one. $40 for the thing and $20 a YEAR for unlimited FREE calls within north america. Good thing is when you take it overseas, you can still call north america free and your friends and family can call you for free as well because u select a north american number, whatever area code you want. If you use it to call international numbers outside north america, you get charged a minute rate (very cheap though). To china its 2 cents a minute.
You plug it in your computers usb drive connected to a BROADBAND internet (dial up doesnt work) and plug a phone into the other end, or you can use your laptops speaker and mic, and just use the phone like a regular phone. You also get free voicemail and it'll send an email to you with a saved voicemail on missed calls when you are away or the computer is turned off. For me and ppl that used it the quality is very good, just like a normal phone, and unbeatable for $20 a YEAR. Give it a shot, pretty cool and the size of a usb drive.
http://www.magicjack.com/4/index.asp