Busy tone - When the button is pressed, 2N® Analog Intercom gives the busy tone

Enter the programming menu
Enter the code for the button memory and wait for a while
The voice menu tells you which number is programmed / check stored number
Check which dialing is set, DTMF or pulse (see the manual, chapter 9)
Check the PBX settings for PSTN numbers in the PBX system, it is necessary to dial prefix (mostly 0 or 9)