BT Infinity Telephone Extension Wiring

A friend of mine recently had Infinity installed and the fitter told him that all existing telephone extension sockets would have to be changed to master types, with a capacitor. This sounds like nonsense to me, particularly as the ID connector on the filter plate is marked 2,3 and 5 with 3 being the bell wire.

Is what the fitter said true?

Mine weren't changed.

Is what the fitter said true?

In short, no. Sounds like they were trying to bodge the existing internal wiring, most likely 2 pair, so nowt spare for the bell wire.