Something

stock Float:ChatSystem(p1,p2)
{
	new Float:x1,Float:y1,Float:z1,Float:x2,Float:y2,Float:z2;
	if (!IsPlayerConnected(p1) || !IsPlayerConnected(p2)) return -1.00;
	GetPlayerPos(p1,x1,y1,z1);
	GetPlayerPos(p2,x2,y2,z2);
	return floatsqroot(floatpower(floatabs(floatsub(x2,x1)),2)+floatpower(floatabs(floatsub(y2,y1)),2)+floatpower(floatabs(floatsub(z2,z1)),2));
}

public OnPlayerText(playerid,text[])
{
new str[86];
new sendername[MAX_PLAYER_NAME];
if(text[0] == ' ')
GetPlayerName(playerid,sendername,24);
format(str,sizeof(str)," %s : %s",sendername,text);
for(new i=0; i<MAX_PLAYERS; i++) if(IsPlayerConnected(i)) if(ChatSystem(playerid,i) < 30)
SendClientMessage(i,COLOR_WHITE,str);
return 0;
}