Smartphones are undoubtedly useful to present day migrants who are fleeing various disasters in the developing world and hoping to settle in more prosperous regions.

I do not however feel that this is of much relevance to those already IN the more prosperous or more developed countries, presumably including most members of these forums.

I cant foresee large numbers wanting to flee say the USA except in the case of an extreme TEOTWAWKI event such as might be caused by a devastating natural or man made disaster.
In such circumstances it seems unlikely that cellphone service would be available.