For each Adapter 1,it can have 3-SIP account and one PSTN phone number,that means each ATA own 4 phone numbers,all can be used as callee at anytime.For the caller,these 4 account can be selected by dial different relevant prefix(including switch to PSTN as an ordinary PSTN phone)
Adapter 1 has a real FXO port to support router call from PSTN to VOIP or from VOIP to PSTN.
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