How to fix snom 300 because it cannot received calls

For the phone incoming calls are originating from where? Things to test to determine the scope of the issue. 1) Can another extension call your extension. 2) If you operate a local VOIP PBX (asterisk, 3CX, etc) if no go to 3. 2a) Are you using a service provider outside of your ISP for provisioning of the Trunk Lines. 2b) If the trunk lines are provided by other than your isp AND they are POTS/Analog lines. The issue is most likely with your trunk gateway 3) If you do not operate your own PBX (Phones connected directly to a SIP or you are using a sip provider for the PBX which is not your ISP and the problem is limited to calls received from outside your network. Because we are referring to calls coming from the outside it would often be an issue with a firewall or SBC (Session border controller) which limits access to your sip services without a defined method to authenticate the inbound connection. Often this is done by port knocking (IE: SIP inbound sends transmission to your network requesting a connection to a certain ext on a specific port at a particular timeframe. The response if rejected and the "real" request for connection is sent to the proper extension and port for connection of the call. (but if the first rejected request was not submitted (i.e.: the knock on a specific port for a specific connection to an extension, at a specific time interval) no one will open the door for the real call. Other types of firewall issues could be only accepting sip traffic from the trunk provider ip range. and likewise the trunk provider will only acknowledge traffic from your companies defines ip range. the trunk provider can also choose to block traffic originating from or transitioning through ip addresses of blocked countries. Lastly your phone needs to have the in bound and outbound details and domains set according to the trunk provider specifications, including supported technology and technology which is rejected. Activating a rejected technology may cause their response to not acknowledge your responses to ring the phone to start with. phone logs may give you some help to see what if failing. For the phone incoming calls are originating from where? Things to test to determine the scope of the issue. 1) Can another extension call your extension. 2) If you operate a local VOIP PBX (asterisk, 3CX, etc) if no go to 3. 2a) Are you using a service provider outside of your ISP for provisioning of the Trunk Lines. 2b) If the trunk lines are provided by other than your isp AND they are POTS/Analog lines. The issue is most likely with your trunk gateway 3) If you do not operate your own PBX (Phones connected directly to a SIP or you are using a sip provider for the PBX which is not your ISP and the problem is limited to calls received from outside your network. Because we are referring to calls coming from the outside it would often be an issue with a firewall or SBC (Session border controller) which limits access to your sip services without a defined method to authenticate the inbound connection. Often this is done by port knocking (IE: SIP inbound sends transmission to your network requesting a connection to a certain ext on a specific port at a particular timeframe. The response if rejected and the "real" request for connection is sent to the proper extension and port for connection of the call. (but if the first rejected request was not submitted (i.e.: the knock on a specific port for a specific connection to an extension, at a specific time interval) no one will open the door for the real call. Other types of firewall issues could be only accepting sip traffic from the trunk provider ip range. and likewise the trunk provider will only acknowledge traffic from your companies defines ip range. the trunk provider can also choose to block traffic originating from or transitioning through ip addresses of blocked countries. Lastly your phone needs to have the in bound and outbound details and domains set according to the trunk provider specifications, including supported technology and technology which is rejected. Activating a rejected technology may cause their response to not acknowledge your responses to ring the phone to start with. phone logs may give you some help to see what if failing.