A post on NKEconWatch has some hard-to-find information about cell phone dialing codes in North Korea. The details show how basic communications controls exist based on the type of account and customer.

SUNNET (2G GSM network, from 2002)

+850 193 801 plus 4-digit number (when being called from overseas)
193 801 plus 4-digit number (when calling SUNNET to SUNNET)
193 801 plus 4-digit number (when calling from Pyongyang “381” landlines to SUNNET)

KORYOLINK (3G network, from late 2008)

+850 192 250 numbers are for foreigners
+850 192 260 numbers are for locals

Pyongyang “382” landline numbers cannot reach SUNNET cell phones.
SUNNET subscribers can call Koryolink “250” numbers but not “260” numbers.

Source: NKEconWatch