A) When the foreign country authorizes it.
NJ2X Note:
Travelling to foreign lands with your amateur radio equipment is one of the wonderful aspects of the hobby. Hams routinely organize special trips to exotic locations for the sole purpose of operating their radios and making as many contacts as possible. These events are referred to as DX Expeditions. Other hams enjoy a more modest approach by simply bringing their lightweight portable radio or HT with them on trips or cruises (see our article, "Flying With An HT").