What is the cheapest American carrier to keep my phone number active for 2FA while living in Bangkok?

Need some specific advice re cell phone plans.. Moving to BKK in July, will have phone paid off and unlocked.. Currently with ATT but their customer service is atrocious .. Will be using AIS while living in BKK.. I’ll have eSIM so can simply toggle back and forth between Asian phone # and American phone # when needing two-factor authentication for banks and the like.. that’s the only thing ill need my American phone # for.. My question is: Which American carrier can i switch to (away from ATT) to keep my American phone # active - with the cheapest plan that will work when needing 2FA ? Not interested in Google Voice or similar.. and not interested in paying $90 per month for an “international plan”, only the cheapest plan /carrier active enough to be able to receive 2FA ? Thanks in advance .

ETA updated with latest post at bottom of thread (if you select ‘All Comments’) on 7/29/24 .