Hello Anees,
welcome to the Polycom Community.
I would suggest you check the SoundStation DUO User Guide => here <= as it clearly states:
The SoundStation Duo conference phone is a dual-mode conference phone that can operate in one of the following standard telephony modes:
• PSTN mode—In this mode, the phone is connected to a standard (analog) phone jack so calls can be made using the Public Switched Telephone Network (PSTN).
• SIP mode—In this mode, the phone is connected to a Session Initiation Protocol (SIP) server so calls can be made over Internet Protocol (IP) networks. In SIP mode, phones can use advanced features such as messaging, forwarding, and transferring.Your phone can be set up to operate in either mode. The mode your phone operates in determines what features your phone will have.
Your phone will only fail over from SIP to PSTN mode. It cannot fail over from PSTN to SIP mode.
Please ensure to provide some feedback if this reply has helped you so other users can profit from your experience.
Best Regards
Steffen Baier
Polycom Global Services
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If official support is required please check how to phone or open a case here
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The title Poly Employee & Community Manager is a community setting and
does not reflect my role. I am just a simple volunteer in the community like everybody else. All posts and words are my own & do not represent the views of Employer.
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Notice: This community forum is not an official Poly support resource, thus responses from Poly employees, partners, and customers alike are best-effort in attempts to share learned knowledge. If you need immediate and/or official assistance please open a service ticket through your proper support channels.
Please also ensure you always check the VoIP , Video Endpoint , Skype for Business , PSTN or RPM FAQ's
