If your building is more than 10 years old, most likely, somewhere in the basement, there is a "panel." It could be in a closet or other area with limited access (but your building manager should be able to give you temporary access). Odds are the fiber will go into the basement in roughly the same area.
Here's an example of the panel.
One one side is the building's internal wiring. Usually, there are two ore more pairs going to each apartment, often to multiple jacks within each one. All of the phone lines entering the building (usually wrapped into single cable) terminate on the other side. Phone company techs then "cross-cut" the incoming phone lines to the building's inside wiring so that each apartment gets its POTS service.
There can be challenges, however. If a former tenant used phone service from a cable company, they may have had the line(s) disconnected at the panel so that the line would not feed back to the AT&T network.
There's also a good chance that the panel doesn't clearly note which pair(s) goes to your apartment. Phone techs can identify them by using a tool that injects a signal into the pair of wires (plugged into a jack in the apartment) and a separate tool, at the panel, that finds the pair with that signal. This sounds more complicated than it is. Not counting the time to go between the apartment and the panel, it takes less than five minutes to identify the pair of wires and do the cross-connect.
If you know someone who does this, they may be willing to handle for a steak dinner or such. If not, I'd recommend asking Sonic's installer if they have any friends in the business who moonlight. Failing that, do a search for "phone systems installation and support" (years ago, I would have recommended checking the Yellow Pages
), but now you can do a web search.
Again, it's trivial for someone with the tools--the hardest part likely is getting access to the panel if it's behind a locked door.
