Question: What is the requirement for E.164 numbers assigned to Mobile Stations (MSs) in a Public Land Mobile Network (PLMN)?
Option 1: They should be unique within the PLMN.
Option 2: They should comply with the E.164 numbering plan in the home country of the MS.
Option 3: They should be composed in such a way that standard ISDN/PSTN charging cannot be used for calls to MSs.
Option 4: They should limit the possibility for MSs to roam among PLMNs.
Explanation: The E.164 numbers assigned to Mobile Stations (MSs) in a Public Land Mobile Network (PLMN) should comply with the E.164 numbering plan in the home country of the MS, allowing standard ISDN/PSTN charging for calls to MSs and enabling subscribers from other networks to call any MS in the PLMN.