The "GoIP" gateways are manufactured by Hybertone. They are not unlike the Portech units that I have used in the past.
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www.hybertone.com/en/pro ··· proid=34All of the details are there, as well as manuals.
This has nothing to do with 3G, Viber, etc. All of that is about cellular data. Using this sort of gateway
you do not send calls over the data channel. You send calls over the voice channel. One active call per SIM that is installed to the gateway.
You exchange calls with the gateway as if it were a SIP or H.323 device, like a multi-port FXO device.
The reference to VPN has to do with the wired network side of the device. It could be installed in the same location as a PBX, or installed remotely and connected to the PBX over a VPN.
I documented my use of a single-port gateway as a backup trunk for our SOHO PBX back when we had such a thing.
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www.mgraves.org/2008/12/ ··· -part-2/