How can the GSM module get the provider's APN?

Question

Circuit design

There is a GSM module, which, in order to use GPRS, needs to get the APN of the provider whose SIM card is connected to it.
The most obvious option is to make an impromptu list in the memory of the microcontroller, and check it against it. But in that case, the possible used providers will be limited to the list. How can universality be achieved? For example, is it possible to get the APN from the SIM card memory?

Answer 1

Yes, the operator's APN is in the SIM memory. Pulled out by AT command.

Answer 2

The provider can have (and has) hundreds of APNs. The available APN for your subscriber is stored in the operator's HLR profile - elementary, if you register some existing APN with the operator, but not registered for your subscriber (in the APN settings in the device / phone) and try to connect, then there are two options: either service, or transfer to the default APN.
The APN is not stored in the SIM memory - it is stored in the device settings.
In your case, it makes sense to have a list of APNs available for public use from operators (or also the APN that the operator issued to you, if any). In this case (even banal phones), they look at the SIM card number (ICCID) and use it to determine the operator according to the list of stored APNs in the phone.
Once again: the APN is taken by the phone from the settings and substituted into the Network Attach Procedure, every time the device tries to connect. In other words, the list of APN can be obtained from the device (and you will register from there), but not SIM cards or networks.