Their faqs (*) state that you need to have an ID or passport from El Salvador, and have a phone number from one of a set of delimited countries, namely :
"El Salvador, USA, Mexico, Guatemala, Honduras, Belize, Nicaragua, Costa Rica, Panama, Spain, Italy, Switzerland, Australia."

It’s not really meant to be a custodial wallet for anybody to use, but rather much solely aimed at their citizens.

Amongst other things I read through on their site and tos today (daily limits, monthly limits, and so forth), the feature whereby its use does not require a data plan, nor does it consume data (but you do need an internet connexion) is still unclear to me.
I figure that the data carriers are obliged to establish the connection and operative for free, and that is likely feasible locally (as per some sort of agreement between the government and the carriers), but I wonder if that applies to those Chivo users residing abroad in one of those countries I cited above (seems like a long stretch).