Swapping AT&T nano SIM card for Orange nano SIM card when travelling to France?

I have no idea what a “prepaid orange” SIM card is or what service it provides but yes, you can swap to a different SIM card when you travel and swap back when you return. If that prepaid orange SIM card is for ATT prepaid service, be aware ATT prepaid does not roam in France. ATT prepaid service will not work in France.

Thank you sandblaster for a quick reply.

Orange is a french carrier (similar to AT&T). I spoke to them and checked that I could get mobile service from them. I wanted to make sure that there wouldn't be some kind of lock from AT&T preventing us from swapping the SIM card. This option would be cheaper for us than the International Day Pass of similar int'l pgms offered by AT&T.

Thank you again!

Unless you specifically purchased and unlocked phone, your device is most likely locked to AT&T. 

You can request an unlock (if you meet the requirements) here: https://www.att.com/deviceunlock/

Thank you, MicCheck for your comment.

I checked with AT&T and the phones are unlocked.

Thank you, again!

You might want to double check that. Go to settings/general/about/carrier lock, if it says “no SIM restrictions”, it’s unlocked.

Thank you, Sandblaster.

This is very helpful.

I checked both phones and validated that Carrier Lock was set to "no SIM restrictions". The AT&T rep didn't mention this when I asked for a way for me to confirm his assessment.