I found the function that sends normal chat messages (those are the messages right? where you can double click their name and it will paste in the Whisper To box?)trunk/src/map/clif.c clif_parse_GlobalMessage
// send message to others (using the send buffer for temp. storage)
WFIFOHEAD(fd, 8 + textlen);
WFIFOW(fd,0) = 0x8d;
WFIFOW(fd,2) = 8 + textlen;
WFIFOL(fd,4) = sd->bl.id;
safestrncpy((char*)WFIFOP(fd,8), is_fake ? fakename : text, textlen);
//FIXME: chat has range of 9 only
clif_send(WFIFOP(fd,0), WFIFOW(fd,2), &sd->bl, sd->chatID ? CHAT_WOS : AREA_CHAT_WOC);
Maybe you could make a new script command that used this code, but instead of AREA_CHAT_WOC, send to ALL_CLIENT.