[Freeswitch-users] How to block CHAT done by using Twinkle

Hi all, Can any one please tell me how to block only a particular SIP packet, especially MESSAGE packet. The reason is, The users are using Twinkle as softphone, and they are able to CHAT with other users. Now I want to disable the CHAT message. When I looked into the logs and sip trace, I found that the packet exchanged during CHAT is "MESSAGE" packet. So is there any way to block this packet alone?? or is there some other way to disable the CHAT??