Yealink SIP-T54S Administrator's Manual page 516

Administrator's Guide for SIP-T2 Series/T19(P) E2/T4 Series/T5 Series/CP860/CP920 IP Phones
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 programable keys:
X=1-10, 12-14 (for SIP-T54S/T48G/T48S/T46G/T46S)
X=1-10, 13 (for SIP-T52S/T42G/T42S/T41P/T41S/T40P/T40G)
X=1-14 (for SIP-T29G/T27P/T27G)
X=1-10, 14 (for SIP-T23P/T23G/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:
X ranges from 1 to 6, Y ranges from 1 to 20, 22 to 40 (Ext key 21 cannot be configured).
Permitted Values:
1 to 16 (for SIP-T54S/T48G/T48S/T46G/T46S/T29G)
1 to 12 (for SIP-T52S/T42G/T42S)
1 to 6 (for SIP-T41P/T41S/T27P/T27G)
1 to 3 (for SIP-T40P/T40G/T23P/T23G)
1 to 2 (for SIP-T21(P) E2)
1-Line 1
2-Line 2
...
16-Line 16
Note: It is not applicable to SIP-T19(P) E2/CP860/CP920 IP phones.
Example:
linekey.3.line = 1
Web User Interface:
Dsskey->Line Key/Programable Key->Line
Phone User Interface:
Menu->Features->DSS Keys->Line Key X->Account ID
linekey.X.value/
programablekey.X.value/
expansion_module.X.key.Y.value
490
Parameters Permitted Values
String within 99
characters
Default
Blank