Motorola Easy Prefix (https://play.google.com/store/apps/details?id=com.motorola.easyprefix) Auto add CSP (Service Provider code) prefix to your phone when you're abroad. https://en.wikipedia.org/wiki/List_of_country_calling_codes This seems to not work correctly and it's generally not a good idea to call home (via GSM) when you're abroad. It's better and cheaper to use chat apps like Signal/Wire)
Phones target this application