Okay then, we're back at the main entrance, over there, by reception, there's a door that goes to the extension and we have further sections such as languages and study desks through there.
The " extension" is an additional telephone that is connected to the same phone number, to the same line, so that two people in one office or one house can both talk to someone.
Each of us was given our own phone extension, too—my phone was a light blue to match my new decor, while Craig's was a manly black—which meant we could conduct our personal business semi-privately.