Straight talk has been using 18 t's Network for quite a while, and I ended up connecting it with straight talk, and it absolutely worked and it worked great.
I just wanted to talk a little bit about using an iPhone 4s, this is an 18t model, and I had it factory unlocked with straight talk.
I years ago actually bought this iPhone 4s used off GameStop, it was a pretty good purchase at the time, and I ended up taking it to straight talk. Straight talk has been using 18 t's Network for quite a while, and I ended up connecting it with straight talk, and it absolutely worked and it worked great.
I use it for a couple years on straight talk, so if you have any questions about an iPhone 4s 18T model, that's factory unlocked working with straight talk. I can tell you if it brings your own device it works, and it works perfectly.
Hopefully, that gives you some confidence if you pick up an iPhone 4s and you want to try it out with straight talk, and you want to bring your own device rather than buying theirs, might end up being a slightly different model than the 18t models.
I can't give advice as to whether that's better or worse, I hadn't researched it but I thought that it was a slightly different model for some reason, but if you bring an 18 t version and it's unlocked it's going to work, and I had no problems with it for a couple years.