I don't think I'm explaining myself properly

I have two "well known" numbers I use for home and office . . . the former is the number all my friends and family use to contact me, the latter is used by by my staff and coworkers. With Vonage, I can simply move both of those numbers to a different Vonage box (and attached "conventional" 2-line phone) at the vacation property through their customer web UI, and my phones ring at my vacation property just as they would at home (they don't ring at home, though).

When I head back to my "normal" home, I can switch them back. There's no need for me to acquire and pay for another number at the vacation property, and when we're not there the phone service is effectively shut down at that location. Some people emulate this functionality by unplugging their Vonage boxes and bringing them with them, but an extra Vonage device at the alternate location eliminates the need to tote one along.

What I'm hoping for is some mechanism (that may include a replacement for Vonage as my VOIP provider), that rings the phones in both locations, and allows me to dial out from either location, without having to make a configuration change each time I move from one property to the other or pay for yet another line. I guess my question is . . . are there VOIP providers that allow you to "mirror" one SIP device to another at a different location, essentially creating a geographically disparate extension phone?