Yealink SIP-T2XP Administrator's Manual page 419

Appendix
when x=14, the default value is 2.
Valid values are:
0-N/A
1-Conference
2-Forward
3-Transfer
4-Hold
5-DND
7-Call Return
8-SMS
9- Pickup
Directed
10-Call Park
11-DTMF
12-Voice Mail
13-Speed Dial
14-Intercom
15-Line
16-BLF
17-URL
Range
18-Group Listening
22-XML Group
23-Group Pickup
24-Multicast Paging
25-Record
27-XML Browser
28-History
30-Menu
31-Switch Account
32-New SMS
33-Status
34-Hot Desking
35-URL Record
38-LDAP
40-Prefix
41-Zero Touch
42-ACD
43-Local Directory
403