Going to be taking a trip to Ireland this fall with either our iPhone X's or depending on timing whatever the 2019 model is called. We did just get our phones unlocked from AT&T though we have yet to do the backup/restore to finish unlocking with the AT&T SIM. However since I didn't realize a backup/erase/restore would have to happen that now has me wondering when we go to put an overseas pre-paid SIM in will that force us to set the phones up and restore a backup as well? That's a LOT of data to pull back down.
