Lifting the handset (or turning on speakerphone) on a Cisco SPA525G2 phone without first entering a phone number immediately prevents dial out, and results in the error message, Line 1 Invalid Number.
Set the Interdigit Short Timer
Best Practice: A simple workaround is to first input the outgoing phone number before lifting the handset or initialising the speakerphone.
To set the Interdigit Short Timer in the phone's web interface
- Obtain the phone's IP address by pressing Menu > 10 Status > 2 Network Status.
- Open a web browser on a computer on the same network as the phone, and browse to the phone's IP address.
- Select Admin login and enter the phone username and password.
- Click Advanced to bring up all available options.
- Click the Regional tab.
- Scroll down to the Control Timer Values (sec) section.
- Update the Interdigit Short Timer with a higher value. This will determine how many seconds you have to dial before the phone gives a busy signal and the error.
- Scroll down and click Submit All Changes. The phone might reboot.
- After the phone has rebooted and come online, lift the receiver (or press the speakerphone button) to test if your timer settings have taken effect.
The phone is not allowing enough time to dial, and going "off the hook." The phone's Interdigit Short Timer needs to be set to an appropriate amount of time.