The UN humanitarian aid will use the +888 interface. From a Q&A by Alec Saunders with Voxbone CEO Rodrigue Ullens:

In cases of humanitarian need, where telephone systems may be inoperable because of natural disaster, the first teams on the ground would deploy a local GSM antenna, connected via satellite to the rest of the world. Then Voxbone would simply forward calls to the +888 country code via satellite to the local GSM station on the ground.

via Joho the Blog » UN gets a telephone country code for disaster relief.