Supplied as a matching pair, The Prelude 121 is a processor controlled telephone with full handsfree operation. The Prelude 121 has the additional feature of a Boss-Secretary intercom system. It may be desk or wall mounted.

Key Features:
  • Intercom
  • Liquid Crystal Display
  • Battery low indication
  • Full handsfree operation
  • Last number Redial
  • Recall
  • Earth Loop or Timed Break (user switchable)
  • Dual signalling: LD (Pulse) or MF (Tone) Signalling (user switchable)
  • Secrecy
  • Ringer volume control (Low, Off or High
  • Intercom volume control (Low Off or High
  • 40 user programmable stores (23 digits capacity
  • Battery protected memory:
  • Power supplied from a 13 amp mains adapter unit
  • Secrecy
  • Timer function
  • Alarm function
  • Pause
  • Message partner
  • Do Not Disturb
  • Exchange

Made by Team Concepts International Ltd (Hong Kong)

Distributed by BT Zones. Supply on both Rental and Sale terms. Sold Prelude 121's can be offered a BT maintenance agreement.
BT UK Trade Sales. Supply on sale terms only.

Approved under Approval Number S/1000/3/N/502623 for use on DELs and PBXs in categories 1, 3, 5 & 7.

Memory will be retained for at least 5 minutes when changing batteries. After this time all 40 memories will clear and the clock will reset to 00.00

Prelude 121 loudspeaking telephones carry a 24 month warranty from date of manufacture as shown on the year and week marking on the base of the instrument (first four digits of the serial number). This is the manufacturers warranty to BT. British Telecom's guarantee to the retail customer is for one year from date of purchase.

Prelude 121 complete with batteries and transformer - BT Item Code 870551

PABX extensions:
When connected to PABX extensions, if the intercom is used and the partner wishes to have an external call transferred to them, the call cannot be transferred over the intercom. The call must be transferred using the normal PABX transfer facility.

Signalling details:
MF Tone signalling: continuous whilst keypad button is pressed.
Timed break recall: 85 milliseconds.
Earth recall: continuous whilst button is pressed. Earth recall: This has 1.5 second duration for long key presses and a duration of 700ms. for short key presses.


To call the extn while holding an exchange line, the ‘intercom’ key should be briefly depressed. If the key is not quickly released, the extn will not ring. This is not a fault, but a design feature of the Prelude 121 which offers facilities of ‘buzz’ or ‘direct intercom on handsfree’ by prolonged pressing of the key.

Users experiencing ringing problems on attempted transfer or enquiry calls should be advised of the above.

While the Prelude 121 can be used as a system pair working to a single line jack, no exchange service will be available to an extn connected only by intercom 5 cabling.

For full facilities each instrument must be connected to its own line jack and the intercom cabling.

The current documentation is not entirely clear on this point, and some customers incorrectly assume calls can be extended over the intercom cabling. The User Guide is to be reviewed and amended where necessary.

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Last revised: April 15, 2021