There is a lot of questions there. I think this post can help

So if you are traveling to US and you only need text for banking, you need to disable both cellular data and data roaming in your phone.

If you don’t want any roaming fee, don’t answer any phone call, check voicemail, use data or send sms,

If you have a phone that does not support VoLTE, you may never get your texts. AT&T, a main Koodo roaming partner, has shut down its older networks.

This is an issue for anyone using a Canadian carrier… Telus, Rogers, Bell, etc.

Thanks for quick replies. My phone is a Samsung Note 9.

So incoming texts don't need cellular data, good to know. Hopefully my phone will receive texts in USA.

This forum helped me and I didn't need to deal with the Chat function and try to get a call back from Koodo which can be very frustrating at times.

Yes to all your questions.

In the US you are going to have to use LTE. I usually recommend turning LTE off to prevent data leakage even when mobile data and roaming data are turned off on the phone. But turning off LTE or VoLTE in the US will leave you without a working phone.

So you may end up with an EasyRoam charge here or there for a Kilobyte or two of data usage. Usually Koodo will refund these without much issue here on the forum or in a callback.