I keep my old phone number active no matter where I go for this very reason (even though it never gets normal use). I have calendar reminders set to tell me to charge it before the number expires. Otherwise you'll have to jump through a bunch of hoops to re-authenticate yourself from a foreign country to any new number you get.
It's easiest just to keep your original cell phone number active indefinitely.
It's easiest just to keep your original cell phone number active indefinitely.