What a helpful reply!
I don't know about mobile phone coverage in the USA, hence brought the topic to a public forum where people generally enjoy spending a few moments helping out a stranger. I do the same for many other topics on various forums on the web, though what I don't do is waste my own time and offer useless advice simply to teach a random person a lesson.
I'm sure I can figure out the 4 major carriers, but as I said, I'm visiting and am not even sure who these big-4 are...!