1)
PNPSCADA supports modems on a public APN.
Having said that, the easiest way to connect a modem to a PNPSCADA server is using a SIM card on the public APN with normal data enabled.
This allows you to get a normal SIM card from your local service provider (should you need one quickly).
However, because of its ability to connect to internet normally, it makes it attractive to thieves.
You can look at prepaid SIMs, so that if it gets stolen, the damage is limited.
Alternatively, for contract SIM cards, you can set up a data-usage limit with your service provider (30MB per month limit is usually enough for downloading profile once per day).
For this method to work the modem needs to be set up to connect out to the server (once per minute).
2)
If you require a Private APN, the easiest is to set the APN to break out to internet.
The problem with Private APNs from my experience, is that if the APN breaks, you have to complain to the Service Provider, until they fix it, where as if you are on the Public APN, if that breaks, everybody complains and they fix it quickly.
For this method to work the modem needs to be set up to connect out to the server (once per minute).
You might also be able to set up with your Service Provider that SIMs on this APN only break out to once specific IP on the internet. This way, thieves wont benefit from stealing this SIM.
3)
If you do not want the modem to connect out to the server, but rather that the server connects to the modem, or if you want a fully private network for your modems, you will require a Private APN. However, for this you will also need your server to get onto that APN.
To get this working, you will need your own PNPSCADA server, and a router with an 3G modem connected to it that can be set to an APN (like MikroTik RouterBOARD 411U).