The modem does not recognize Korean SIM cards (what?)

[bdicewk]

I visited a shop of the phone provider today, and they did something in their system (not with the phone or the sim card), and the sim card started to work (quite buggy though). I cannot be sure if their changes in the system made the phone recognize the sim card, or this is just a concidence, but none of these sounds completely reassuring for me: if this is a coincidence, then I still don't know the real root cause of the problem. And if this is not a coincidence, then this does not look like quite a well design, because the *detection* of the SIM card actually requires some interaction with the network.