Yealink SIP-T21 E2

Administrator’s Guide for SIP-T2 Series/T19(P) E2/T4 Series/T5 Series/CP860/CP920 IP Phones
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To connect the expansion PSTN box:
For CP860：
1. Insert the USB plug on the expansion PSTN box into the USB port on the phone.
A PSTN box:
Two PSTN boxes:
For CP920：
1. Insert the USB plug on the expansion PSTN box into the USB port on the phone.
A PSTN box: