Thanks for your help Tony
I admit I didn't think of leaving the Inbound CID pattern blank
I've just run a new test like suggested but it didn't work out as supposed: when I ring Eutelia's inbound number all I can hear is a series of bips, the same thing that happens when you get a network error!
I tried different variations for the forwarding number:
0039 123 456789
+39 123 456789
#0039 123 456789
I always get the same result!
Am I missing something?