Call waiting function can be disabled by telnet command “voip sip cw”.

> voip sip cw
usage:
%voip sip cw [endpoint] <value>
current call waiting status: ep1: disable

> voip sip cw 1
>voip sip cw
usage:
%voip sip cw [endpoint] <value>
current call waiting status: ep1: enable

> voip sip cw 0
> voip sip cw
usage:
%voip sip cw [endpoint] <value>
current call waiting status: ep1: disable