When you travel internationally, you should leave your mobile phone and laptop at home. You can rent phones at most international airports that include data plans.
I’ll never bring my phone on an international flight again. Neither should you.
Quincy Larson

If you have an iPhone, with iOS10 iCloud backups are very good now (I’ve done 1/2 dozen restores in the past month — no issues).

So this is how to take your iPhone:

  1. Backup to iCloud
  2. Reset and your phone
  3. Restore as a new phone (don’t enable icloud)
  4. Cross Border
  5. Reset and Restore iPhone backup from iCloud
  6. Smile :)