What kind of Sim card does the iPhone XR take?

I plan to get a Product Red iPhone XR 128GB for Christmas, I'm getting it unlocked and plan to use it with Straight Talk(I can't afford the big name providers like Verizon, T-Mobil, AT&T and Sprint), so what kind of Sim card does the iPhone XR take?

IPhone X water damage question? - 1

Here are the details; I went into the hot springs for 30 seconds max, in less than 3 feet of water. So I thought my phone would be fine, I got out, everything worked, and I thought I was good, but then my phone started glitching green so then I turned my phone off, the touch screen worked just fine. Then I put it in rice and after 2 days heard that wasn't a good idea. So I pulled it out and turned it on and the phone was no longer Green, I thought I saved it, the. It died right there and now every time I turn it on, the apple logo turns on then turns off then it does it again Over and over again. So I put it in front of a cool fan to dry for 3 days, now I'm here. I tried to factory reset the phone because I read that it worked on apple forums, and now it just says plug into iTunes because when I try to finish the process it turns off. So now i'm wondering what my costs and problems are. The phone was $1300 and now it's $1200. It's 256gb and I don't wanna lose it. Any help would be greatly appreciated. The touch screen does work, the Face ID said it wasn't able to work and I noticed a lot of fogging in the front and back camera lens, but it's gone now that I fully dried the phone.

Can you collapse while in a lying position?

This is really a question related to semantics rather than medical terminology. Anyway, I wanted to know how it is called when e.g. A person is lying on the bed and does something, such as texting on the iPhone or reading a book, and just all of a sudden he/ she faints and drops his/ her arms down, as well as whatever he/ she was holding. Would it be correct to say that the person collapsed after fainting, even though he/ she was in a lying position? Or does the fainting make you collapse only when you were previously standing, sitting, kneeling, crouching, or whatever?

Can a prepaid iphone be used for a non prepaid account by replacing the sim?

Can a prepaid iphone be used for a non prepaid account by replacing the sim?

Added (1). I should mention, both the prepaid phone and the existing sim from another phone are on AT&T network.

Added (2). What I'm really trying to do is upgrade from my existing iphone SE to an iphone 8 by buying a prepaid iphone 8 that is on sale for a great price.

IPhone 7: Why is my ringtone playing when I click into Settings?

Just wondering if anyone knows how to fix a glitch in iPhone 7. When I go into settings, my ringtone sounds out of nowhere. Doesn't happen every time but most times. So no matter what I'm going into settings for ringtone usually plays once for some reason.