Thanks, @syaoran. I appreciate your input!
I am not sure what AT&T and Verizon offer in terms of taking international credit cards. Countries not on the list can be due to a lot of reasons. One of which, is fraud prevention and another, not having any banks from Singapore in the US. Barclay's is a common one accepted across Europe and they do have banks in the US. Their cards works from the countries listed. However, some other banks in the same countries do not.
When arriving in the US. Most major airports have cell shops right in the airport. You could always stop in a store once you land and buy a SIM or eSIM from one of them. Amazon.com or BestBuy.om might offer more options.fpr you to purchase internationally before arriving in the US.
Thanks for your reply, @syaoran. Not sure if you are allowed to in this forum, but if you do, will you be able to let me know which other service providers in the US allow me to buy an eSim plan online while still in Singapore for my use in the US as a tourist?
If your country isn’t listed and the address on file for your credit card is in Singapre. The transaction will more than likely not process. Even the countries that are listed, whther a card works or not can be very hit and miss.