Yealink SIP-T54S Administrator's Manual page 1045

Appendix
X ranges from 1 to 6, Y ranges from 1 to 20, 22 to 40
(Ext key 21 cannot be configured).
For line keys:
Valid types are:
0-N/A
1-Conference
2-Forward
3-Transfer
4-Hold
5-DND
7-ReCall
8-SMS
9-Direct Pickup
10-Call Park
11-DTMF
12-Voice Mail
13-Speed Dial
14-Intercom
15-Line
16-BLF
17-URL
18-Group Listening
20-Private Hold
22-XML Group
23-Group Pickup
24-Multicast Paging (Paging)
25-Record
27-XML Browser
34-Hot Desking
35-URL Record
38-LDAP (only appear when the parameter
"ldap.enable" is set to 1)
39-BLF List
40-Prefix
41-Zero Touch
42-ACD
45-Local Group
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