Think of it this way. The ip phone in DC connected to the TDA in Colorado would be like streching a long line cord from the pbx to the phone. All calls originated from the ip phone would use the resources (lines) in Colorado. If DC dialed 911 from the ip phone, it would appear to the psap as though the call originated in Colorado. So if you are not needing a published number for DC and calls went thru an 800 number in Colorado, that might be ok. If you need to have a published number in DC and some sort of connectivity to Colorado, then you would have a system at both locations, and connect them via gateway cards/resources.
Sorry if this is too basic, but sometimes understanding ip connectivity needs to start at square 1.
