Add a beep because my PBX kept crashing, & phone doesnt ring,
My isdn log shows the call, so if I get a beep, I can realise,
& cold reboot my crashed PBX.
Deutsche Telekom reports to callers: 
	From public call box:	Line engaged beeps
	From isdn phone with display "Teilnehmer zur Zeit nicht erreichbar"

# *** 4.4-RELEASE/src/usr.sbin/i4b/isdnd/support.c	Wed Aug  1 19:45:03 2001
# --- jhs/src/usr.sbin/i4b/isdnd/support.c	Thu Nov  8 10:57:48 2001
# ***************
# *** 549,555 ****
#                   src_tela = get_alias(mp->src_telno);
#                   dst_tela = get_alias(mp->dst_telno);
#   
# ! 		log(LL_CHD, "%05d Call from %s to %s",
#   			mp->header.cdid, src_tela, dst_tela);
#   	}
#   	else
# --- 549,555 ----
#                   src_tela = get_alias(mp->src_telno);
#                   dst_tela = get_alias(mp->dst_telno);
#   
# ! 		log(LL_CHD, "%05d Call from %s to %s",
#   			mp->header.cdid, src_tela, dst_tela);
#   	}
#   	else

# *** 7.0-BETA2/src/usr.sbin/i4b/isdnd/support.c.~1~	Sat May 13 14:42:55 2006
# --- jhs/src/usr.sbin/i4b/isdnd/support.c	Tue Nov 20 20:20:52 2007
# ***************
# *** 668,675 ****
#                   src_tela = get_alias(mp->src_telno);
#                   dst_tela = get_alias(mp->dst_telno);
#   
# ! 		llog(LL_CHD, "%05d Call from %s to %s",
# ! 			mp->header.cdid, src_tela, dst_tela);
#   	}
#   	else
#   	{
# --- 668,675 ----
#                   src_tela = get_alias(mp->src_telno);
#                   dst_tela = get_alias(mp->dst_telno);
#   
# ! 		llog(LL_CHD, "%05d %cCall from %s to %s",
# ! 			mp->header.cdid, 7 /* bell */,  src_tela, dst_tela);
#   	}
#   	else
#   	{
================
The above patch does not apply on 4.11, but I dont care, my gates now use 6.2 or so.
Patch also doesnt apply to 6.3, but
I'm now 2008.02 patching this out , cos too many random beeps in this office from unknown devices.