I found enable_heartbeat_events variable can help this case. <action application="bridge" data="{enable_heartbeat_events=5,nibble_rate=1,nibble_account=0838833133}sofia/external/$1@tel.co.th"/> it's work fine. I update http://wiki.freeswitch.org/wiki/Mod_nibblebill already Dome C. 2009/7/18 Dome Charoenyost <dome@tel.co.th>:

Dear sir,

     I found some problem when try to enable nibblebill in B-Leg      My Dialplan

     <action application="bridge" data="{nibble_rate=1,nibble_account=0838833133}sofia/external/191$1@203.xxx.xxx.xxx" />

     problem is niblle do nothing until hanup call. i try to debug nibblebill and found some issue. nibblebill can't get billrate , billaccount from channel

       billrate = switch_channel_get_variable(channel, "nibble_rate");        billaccount = switch_channel_get_variable(channel, "nibble_account");        if (!billrate || !billaccount) {                return SWITCH_STATUS_SUCCESS;        }

Dome C.