It seems that all FXO lines are configured as shared FXO line. You just need to press the shared FXO phone button and directly dial out without dialing steering digit.
Please run impedance matching tool at FXO Ports page. If it doesn't help, test with the ananlog phone or switch the working phone line to the 2nd and the 3rd FXO port to see if the issue follows FXO port or FXO phone line.
It is perfect fine to configure all FXO lines as separated shared FXO lines and assign individual PSTN numbers. Are these 3 FXO lines are with the same service provider? If you hook an analog phone to the phone line, what are the dialing plan you can dial out? Do you need to dial the steering digit? If yes, then the service provider sets the UC320W as the centrex PBX.. Please let me know. I will send you a PMF to correct the FXO line dial plan. When you press the shared FXO line button 2 or 3, do you hear the stutter tone or normal dial tone? If it's stutter tone, the FXO line may be configured with voice mail service by your service provider and there are voice messages. It may affect the call to be dialed out.
If you can't figure cout what it is going on, please contact the Small Business Support Center at the phone number listed (Please pick the appropriate phone number in your region) in the link attached. One of our Engineers should be able to assist you with this issue.
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