X ranges from 1 to 2 (for SIP-T21(P) E2)
For programable keys:
X=1-10, 12-14 (for SIP-T48G/T46G)
X=1-10, 13 (for SIP-T42G/T41P/T40P)
X=1-14 (for SIP-T29G/T27P)
X=1-10, 14 (for SIP-T23P/T23G/T21(P) E2)
For ext keys (only applicable to SIP-T48G/T46G/T29G/T27P IP phones):
X ranges from 1 to 6, Y ranges from 1 to 20, 22 to 40 (Ext key 21 cannot be
configured).
When assigning the following features, you do not need to configure this
parameter:
1-Conference
2-Forward
3-Transfer
4-Hold
5-DND
7-ReCall
8-SMS
9-Direct Pickup
11-DTMF
17-URL
18-Group Listening