Hi,
what's the idea of using the SPA-3102?
If you going to use it with 3CX server, you can use a PSTN line attached to 'Line' port of the SPA-3102 and an analog telephone attached to 'Phone' port of the SPA-3102. You make normally 2 registrations of SPA-3102 - one as PSTN device (for FXO port) and one as extension for FXS port. In this way you can receive / make outgoing calls to/from the 3CX server and also use (like another device) the analog phone attached to FXS port, like any other extension in the 3CX PhoneSystem.
If your device has been configured for a VoIP provider, normally you will make/receive VoIP calls from/to FXS (Phone) port. The FXO (Line) port will be used normally for backup through your PSTN line (if any), allowing you to receive calls from PSTN line to analog phone and made outgoing calls via PSTN line (with some code like '#', depending on your provider, or automatically if no VoIP service, or different routing (VoIP or PSTN) for different destinatons).
If this is the case you can not use the SPA-3102 with your 3CX system, unless you reset it to factory default (you will loose your current provider settings).
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In other (more technical) words there are four ports into SPA-3102:
(1) LINE
(2) FXO_VoIP
(3) FXS_VoIP
(4) PHONE
You can configure the SPA-3102 for the following seven type of calls between them (2 independent calls at one moment), not all types possible simultaneously:
(1) >> (2)
(2) >> (1)
(3) >> (4)
(4) >> (3)
(1) >> (4)
(4) >> (1)
(3) >> (1)
If case of provider, normally you are allowed to make only:
(1) >> (4)
(3) >> (4)
(4) >> (1) or (3)
If you use it with 3CX (or other IP PBX) you will have the following types:
(1) >> (2)
(2) >> (1)
and independently
(3) >> (4)
(4) >> (3)
Calls like (1) >> (4) and (4) >> (1) possible through 3CX only, nevertheless you can still make (4) >> (1), but not recommended.
See SPA-3102 admin guide for details (available from Internet - Cisco site).
Regards