My husband and I have had Vonage for over five years. We've never had a phone bill that exceeded the $24.99 per month. We kept our original phone number with absolutely no problem. We can check our voicemail messages from the computer if we want to (like when we're out of town). Online Vonage keeps track of all incoming and outgoing calls with the telephone numbers - so you always have a record of who called who when. (Very useful if you're taking legal action against telemarketers.) We are both former military and have friends and family all over the country - so we have hundreds of hours of long distance usage every month.
We LOVE Vonage.
The downside: When the power goes out, your phone goes out. I suggest that you keep an "emergency phone" plugged into the phone jack. (If the power goes out you can still dial 911 even if you have no phone service.) Vonage is also not automatically hooked up through the 911 service, so you have to go online to Vonage.com and register your telephone number and address through the 911 service in your area. (This is a one time thing and only takes a few minutes.)
If you have any other questions, please let me know!