don't raise exception in case of MSC->MGW IAM
diff --git a/src/mgw_nat.erl b/src/mgw_nat.erl
index 274cedf..0514900 100644
--- a/src/mgw_nat.erl
+++ b/src/mgw_nat.erl
@@ -116,7 +116,10 @@
replace_isup_party_prefix(PartyNum, ?MSRN_PFX_STP, ?MSRN_PFX_MSC);
_ ->
PartyNum
- end.
+ end;
+% default case: no rewrite
+mangle_isup_number(from_msc, _, _, PartyNum) ->
+ PartyNum.
% replace the prefix of PartyNum with NewPfx _if_ the current prefix matches MatchPfx
replace_isup_party_prefix(PartyNum, MatchPfx, NewPfx) ->