Broadband Phone system

I am thinking about setting up a broadband phone system for our house. I am interested in saving some money from from our current $60 a month from SBC. We currently have Unlimited local and long distance, voicemail, call waiting, caller id, call waiting id, and privacy manager. It seems that the broadband phone services offer the same features for about $30 a month.

I am really interested in Vonage and their Premium Unlimited Plan. Vonage offers some great, and what I think is required, features:

1. Keeping existing phone number
2. Dialing 911
3. Network Available number (phone number that will calls get transfered to when network is down)

I do have some concerns, that I need to look into before I sign up for this:

1. Make sure that when I transfer my number from SBC to Vonage, I can get a new number for my existing phone line, as opposed to service being cancelled.
   
• I want to keep this line for our ADT system
  
• To have a phone line in case power goes out
2. Make sure that I can plug the phone adapter into my punch down block, so I can use this line for the whole house.