got it, joe thanks for leading me in the right direction.
always look very carefully at the output in asterisk CLI !
Anyhow, two things caused that strange silence behaviour:
1/ Its not that there is a silence caused by the carrier, but because Asterisk since v1.4 changed their default MusicOnHold directory from /var/lib/asterisk/mohmp3 to /var/lib/asterisk/moh, but A2B 1.4 still refers to the old directory by default, most probably, copying those music files at least gives you music instead of silence.
http://www.freepbx.org/forum/freepbx-di ... ic-on-hold2/
But the question remained, WHY the heck did the international calls play moh and local ones did not...
WHY is ${MOHCLASS} being set, which results in playing moh.
[macro-dial]
exten => s,1,GotoIf($["${MOHCLASS}" = ""]?dial)
exten => s,n,SetMusicOnHold(${MOHCLASS}) <-------- THIS IS THE CULPRIT
It is the same dial string for national as international calls, but the international cals are calling MOH and local are not.
And the solution is.....
switch in the web admin panel (a2b) to advanced mode.
key: advanced_mode
value: yes
that will show You on the rates window, the correlation between a rate and a music on hold class (a2b has several of these created by default).
Once You switch to this mode, ensure that Your destinations have "No Music on hold" set, and all is fine and dandy !
NO MORE SILENCE.