Before trying next, as starting point: have you checked date and time (not using NTP?) settings on each device involved (I mean on Patton 4112, on Asterisk and on IP phones)?
I’m not using an NTP because there’s no internet connection at the moment and there are no internal NTP server.
Did you looked also for new SNOM 760’s available firmware (the same could be asked about Patton 4112 R6.3 against R6.5 even if the Patton 4112 configuration looks good indeed both GrandStream and the others soft-phones tested are able to complete outgoing calls to PSTN number)?
That’s a good suggestion, I will update the fw immediately.
The SNOM 760 seems to behave differently than Grandstream looking at the logs provided. Is it correctly and properly registered on Asterisk+FreePBX?
Yes.
I’m not an expert on Patton 4110 Series or on VoIP over SIP trunking to ITSP provider (Italian VoiceOne in this case) but if I were you I will for sure start checking those aspects before go deep on logs.
The strange fact is that the other telephones work so I’m pretty sure that Patton configuration is good. Anyway, I will check it again, thanks for the help.