Try changing the dialing digit detection setting on the VG port. This documentation is less than crystal clear, but it is worth a try.
Changing the Dialing Digit Detection
The VG248 detects DTMF tones when users press the keys on their telephones. However, if the VG248 is having difficulty detecting the DTMF tones on some phones, you can change the dialing digit detection setting.
Changing this setting enables the VG248 to recognize the DTMF tones when users press the keys to make a new call. However, once the call connects, the VG248 might fail to recognize the DTMF tones again if users need to navigate through DTMF-driven menus.
default: use DSP
alternate: use SLIC
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