> Based on the office phones I've used, I'm guessing that the buttons with the 7-digit phone numbers are just used to select phone lines that this phone can mak

> Based on the office phones I've used, I'm guessing that the buttons with the 7-digit phone numbers are just used to select phone lines that this phone can make/receive calls on, not speed-dial numbers. I'd also guess that they're on an internal military phone network that's not directly reachable from the regular phone system. Yeah, listing both lines there also might allow this phone to "barge" in on an existing call on one of those lines. If one is in use, it might show up in a different color, allowing the user to select the unused one if they wanted a new line, or the used one if they wanted to join in on the call in process on that line.