No audio from incoming external calls

[CTOSHRP]

So from my network I can call outside numbers and those lines are all sending/recieving audio fine. 

When someone calls in, there is nothing heard on the line. 

Is there any specific messages in the debug for the router that I should be looking at for this, I cannot find much information online. 

[John Steele]

Most issues of this type are almost always network related; i'm assuming the call is connecting and you are not hearing audio.  Any chance you are not allowing RTP traffic inbound?  maybe check the firewall logs for UDP range 16384 and 32767.  The doc below shows many of the commands you can do on your CUBE.

Troubleshoot No-way Audio Issue with Hairpin Calls on CUBE - Cisco

Troubleshoot One Way Audio Issue Using CLI Debug Outputs from Cisco IP Phone 7800/8800 Series - Cisco