asterisk users - Sep 2003 - help asterisk call waiting X100P -> MGCP ata 186

I am running CVS-09/11/03-14:03 on Redhat 9.0

Trying to get call waiting / call waiting callerid working.
The setup is:
X100P asterisk -> ATA 186 MGCP --> analog phone.

How do I answer the call waiting beep..

Thanks, I appreciate any help.