Audio - What to check if You can't hear the ring-back tone?

Please check that you have latest firmware version (download section) and following settings:

• Delay for ALERTING in GSM outgoing groups is set on 1 and higher

If you enable Virtual Ring Tone in GSM outgoing groups you must set Ring Tone in GSM basic parameters so gateway knows the tone to generate. Be aware that this setting overrides Ring tone (which can also contain e.g. the information that the calling party is not reachable, notice about transferred number, ringing tone etc.) and replaces it by the virtually generated ringing tone.