I've had Vonage for a couple years now. I have their 500 minute plan which is around $20 month total. There is no long distance for US, Canada, and alot of Europe and other places. My wife can call her family in the Philippines for like 9 cents a minute. You need a high speed internet connection, and you can enroll on their website.
As for 911 service, at the time you setup an account, you are also prompted to register your number in the 911 system which I have done, so that if I call 911, they will know from who the call came, and the location. If you don't register, you will not be in the 911 system. You also get caller ID and voicemail just like a cell phone service.
For me it worked out that I could get Vonage phone service along with Roadrunner internet for about the same price as a land line, so if you are on a phone line based internet service its a major step up.