How to switch from an iPhone 6 to a flip phone temporarily?

I have an iPhone 6 that is on it's last leg and I still have four months left on my contract. How can I use an older phone, like a flip phone, and keep my phone number? I only want to do this until my phone is off contract and I can get a new one. Is it possible? The iPhone 6 uses a nano SIM and does not fit into any kind of Micro SIM holder.

Do I have to sign up for Facebook messenger in order to send/receive inbox messages?

When I looked up a classmate I haven't seen in years, I sent a message to her inbox. Even though the message is clearly there and time/datestamped when I go to "messages" (which is now the "FB Messenger" button, thanks to Facebook's upgrade), I'm not sure if she is capable of receiving it, since I didn't sign up for Facebook messenger. It's kind of confusing, because when I attempted to inbox her on my iPhone, I was forced with the option of signing up for FB Messenger. So I went to my computer instead, where I was able to inbox her without having to sign up for that.

Can a person who has Facebook messenger still receive messages in their inbox from people who haven't signed up for FB Messenger?

I looked up a classmate I haven't seen in years, but the "Add Friend" button was not on her page, as she obviously disabled that function. So sent a message to her inbox. Even though he message is clearly there when I go to "messages" (which is now the "FB Messenger" button, thanks to the upgrade), I'm not sure if she will be able to see it. It's kind of confusing, because when I attempted to inbox her on my iPhone, I was forced with the option of signing up for FB Messenger. So I went to my computer instead, where I was able to inbox her without having to sign up for that.

Added (1). Even though THE (not "he") message is clearly there…

Why do people on welfare have nice cars purses iphones etc

It really doesn't make sense to me. People on welfare can somehow afford fancy things like nice cars, purses and iphones. BUT NOT FREAKING FOOD. Really? I'm So GLAD that this is what my taxpayer money is going towards, buying some welfare queen's iphone plan.

Why do naps make me more tired?

Whenever i take a nap, i will sleep for like 3-4 hours, but whenever i wake up, i'm twice as tired as i was before! Does anyone know why this would happen? What can i do or take that would help me wake up non-cranky-like and rested?

Are iPhone 7+ dangerous? Will they cause fires?

Are iPhone 7+ dangerous? Will they cause fires? - 1

Added (1). I was letting it charge while taking a bath. In the middle of a text, it started making sizzling noises and could swear I saw smoke. I banged it on the edge of the tub a few times and it seemed to be okay. Any idea if this is safe?