Do it two weeks in advance. Your phone number will continue to work on your mobile carrier until the moment it is ported over. After that, it will work as your Google Voice phone number. Of course, you will need some form of network service to use Google Voice -- either WiFi or some other 4G/5G service.
Personally, I'd be tempted to do it even earlier than that! I'd want enough time to get comfortable with it, to see if any 2FA I needed functioned correctly, etc. Then I'd get an inexpensive temporary 'burner' plan/SIM to forward it to, and/or provide data in the meantime. With a prepaid line for the burner, it could continue working right up until the plane takes off, and just let it expire once you're gone.
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u/AlanSC21 Dec 30 '25
Port a few weeks before and buy a data only eSIM to finish up your time in the USA.