VoIP link to cellnetworks & One SIM, 2 numbers

I would have preferred to post this in the offtopic forum since it is regarding services around Asterix rather than a technical subject involving Asterix directly.

I have noticed innovators in international simcard operators.
Some are offering 2 numbers in one simcard, even with roaming and another is offering some kind of VoIP intergration.

I don’t suppose you have any ideas on the technicalities behind such new setups, or what to search for for more info?

AFAIK the dual number ability is part of the GSM standard but the VoIP linking sounds intriguing.

I don’t believe there is any requirement for SIM cards to know the phone number at all. Addressing is done by the IMEI, and even in the network, routing is done using a roaming number. Obviously there is a facility, as part of the directory functions, to display own number, but that is, I believe, optional.

For inbound calls, I suspect this is done within the HLR. For outgoing calls, I suspect they are using some sort of sub-address facility, like the ISDN sub-address.

There are devices that switch control between two SIM cards.