[gmmour]

The fact that they had international roaming in North Korea by declaring their IMSI and phone number probably has nothing to do with their native provider, since there is no provider I know that has roaming agreements with North Korea...

So incoming calls are probably not an option, unless the North routes the incoming calls to their roaming visitors as if they were coming from e.g. China (i.e. as if those roamers where roaming on a network that has an actual roaming agreement with the roamers' native network).

For outgoing calls now, it is known that GSM phones can be tricked to "think" that they're connected to their Home network, since there is no authentication of the network to the phone (on 3GSM this is solved and USIMs also verify the authenticity of the network they are connected to, but there is no 3GSM in N. Korea anyway).

Anyway, it is very weird to hear that one can have roaming in N. Korea. For outgoing calls, this is possible with "tricking" phones to believe they're on their home network (of course this will actually mean that North Korean towers transmit the MNCs of all possible networks of current visitors in the country), but with incoming calls, this needs the cooperation of North Korea with a network (most probably a chinese one) that has a roaming agreement with the roamer's home network... I do think that it is not inside the Chinese networks' roaming agreement terms with foreign networks, to offer this virtual roaming to people visiting North Korea.