While a lot of telecoms cabling now gets combined in with general cat5e data cabling, there is still demand and use for the tried and tested products such as:

Line Jack Units - standard BT plug type telephone sockets in PSTN, PABX and slave formats. These come in compact singles, singles and doubles, so there are lots of options, 2/1A, 2/2A, 2/3A, 3/1A, 3/2A, 3/3A, 4/1A, 4/2A, 4/3A. The current main house type telephone socket, the NTE5, is available in stock and is the same make as BT use.
IDC junction boxes 77a (3 pair/6 wire) 78a (4 pair / 8 wire)
Connection boxes for 10 pair (237A) strips. Sizes from 20 pair to 100 pair in stock and other sizes on request. Internal and external.
Telephone cable in many pair sizes and types, from 2 pair to 100 pair, including internal, external, armoured and overhead CW1308, CW1128.
Connectors and plugs BT431A/BT631A (normal BT type telephone plugs) RJ10/11/12 (clear RJ type plugs) 8A/8B jelly crimps (external joint connectors)