Jon,
If you are looking for a complete service provider, you can check out Vonage (www.vonage.com) or Primustel (www.primustel.com). There are probably about a dozen or more that provide the complete service. If, however, you want to go the route of having a gateway in your house and one at your office so that you can call over IP to your office and the “hop-off” from your office to all long distance, then you would be looking at Quintum or Cisco, though some of the features would be dependant on your PBX.