External Phones not ringing through

[apex.tech]

running cisco unified communications manager 7 with multiple sites.  For some reason, starting last week, one of the sites stopped being able to make or receive external calls.  When you call any of the lines, they go straight to voicemail.  When users try to call outside the company it goes silent and nothing.  They can however make and receive calls to internal extensions.  Originally we were told that it was because the phones were registered to the router rather than the call manager, but that has since been proven incorrect.  Any ideas??

[Andrew West]

What is your method for PSTN connectivity? 

[Jaime Valencia]

Start by debugging your GW for whatever method you use to reach the PSTN to see if the call is making it that far, and if it is, disconnect cause to then review the related config, if it's not even making it to the GW, review all the relevant CUCM config.