I didn't see it mentioned there, so I have to ask: what about the cabling? Depending on where the telephone cables entered the building, they would have to get up to 12 meters longer. How did they make that work? Did they splice every cable? Or did the cables already have enough slack?
That depends very much on where the cables were running. Some of them will have gotten longer than needed, others shorter and for some it may not have made a big difference, merely a slight change of angle.
The phone companies deal with cable splices all the time (roughly at the rate of backhoe deployment), so they most likely shut down the trunks one-by-one, extended the ones that needed more wire and they may or may not have decided to take up the slack in the remainder (to avoid parasitic inductance and capacitance from rolling up the excess wire).