[IAD-300] When the VoIP enabled, how do I dial the PSTN call via IAD-300?

After you enable the SIP VoIP function, you can pick up the handset and dial the VoIP call directly. But if you want to make a PSTN call, you need to dial the PSTN Prefix number first. The default Prefix is “0*”.
For example, the local PSTN number is “22199122”. You need to dial as below steps.
1.Pick up your handset on the phone.
2.Dial the “0*”, you can hear the tone will be changed.
3.Now you can dial the PSTN number “22199122” and press “#" to make a phone call immediately.