Yealink SIP-T54S Administrator's Manual page 667

Configuring Advanced Features
Parameters Permitted Values Default
For SIP-T27P/G IP phones:
The default value of the line key 1-6 is 15, and the default value of the line key 7-21 is 0.
For SIP-T40P/T40G/T23P/T23G/T21(P) E2 IP phones:
The default value is 15.
For ext keys:
For SIP-T54S/T52S IP phones:
When Y=1-60, the default value is 0 (NA).
For SIP-T48G/T48S/T46G/T46S IP phones:
When Y= 1 to 40, the default value is 0 (NA).
For SIP-T29G/T27P/T27G IP phones:
When Y= 1, 21, the default value is 37 (Switch).
When Y = 2 to 20, 22 to 40, the default value is 0 (NA).
Note: It is not applicable to SIP-T19(P) E2/CP860/CP920 IP phones.
Web User Interface:
Dsskey->Line Key->Type
Phone User Interface:
Menu->Features->DSS Keys->Line Key X->Type
linekey.X.line/ Refer to the following 1-16 correspond to
expansion_module.X.key.Y.line content the lines 1-16
Description:
Configures the desired line to apply the BLF List key.
For line keys:
X ranges from 1 to 29 (for SIP-T48G/S)
X ranges from 1 to 27 (for SIP-T54S/T46G/T46S/T29G)
X ranges from 1 to 15 (for SIP-T42G/T42S/T41P/T41S)
X ranges from 1 to 21 (for SIP-T52S/T27P/T27G)
X ranges from 1 to 3 (for SIP-T40P/T40G/T23P/T23G)
X ranges from 1 to 2 (for SIP-T21(P) E2)
For ext keys:
For SIP-T54S/T52S:
X ranges from 1 to 3, Y ranges from 1 to 60.
For SIP-T48G/T48S/T46G/T46S:
X ranges from 1 to 6, Y ranges from 1 to 40.
For SIP-T29G/T27P/T27G:
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