Switched from Straight Talk to Mint Mobile this afternoon, here's my experience:

Tl;dr enormous success, it took 10 min to move my phone number to Mint Mobile.

Album of screenshots: https://imgur.com/a/ZjKRKnT

I’m on an iphone 5c, upgrading to the iphone Xr before the new year.
My wife knew I had the Mint Mobile trial in my Amazon wishlist, it's only $5 and they say you get your $5 back if you sign up for a plan. I tried the trial today.

Before I switched I did a fast.com speed test on LTE while Straight Talk was my carrier.
Straight Talk Speed Test Result: 2Mpbs
Mint Mobile Trial Speed test result: 38Mbps (but then I ran out of data haha whoops!)
At home we have the cheapest Verizon Fios wifi 50Mbps and it works great for two laptops, two iphones and a roku streaming pluto.tv’s train channel.

Activating the trial sim card was SO simple. I put it in, followed the steps, it had me use the camera to scan the barcode on the sim card so I didn’t have to type the long number into the box. The app asked me to change a few things under Settings>Cellular. I didn’t have to change any settings though. This kind of confused me because I was looking for what I needed to change and there were no boxes with information to edit. This could be because I ported this phone from Verizon to Straight Talk about 4 years ago? Setting up Straight Talk took about 3 days; you can see why I’m so excited about Mint Mobile working so well!

In settings where I see “cellular” I now see two more settings, “Personal Hotspot” and “Carrier”. These settings remained after I activated the three month plan. Under the carrier setting it says Network Selection: automatic. Maybe this explains why I didn’t have to edit any settings.

I made a few phone calls on the trial and checked out the stats the app could tell me while in the trial. I'll post that screenshot later.

I decided Mint Mobile worked so I made the switch, plus I could always go back to Straight Talk if it was not as promised. So I went into the Mint Mobile app and hit the button that said “Let’s make this official” or some cute phrase like that.

To transfer the number I needed several things: your account number, phone number, pin number on your account, and zip code. My account number in Straight Talk’s system, is the IMEI number. You can find your IMEI number by dialing *#06# on your phone.

I screenshotted all of the screens I went through to activate the three month plan. The total cost with tax came to $48.53, I live in Pennsylvania. I took screen shots for two reasons, first to show other people the process, second to pull the time stamp off the screenshots. Album here: https://imgur.com/a/ZjKRKnT

It took exactly 10 minutes to transfer my number (port the number) from Straight Talk to Mint Mobile through the Mint Mobile App on wifi after activating the trial.

Once my phone number was activated with Mint Mobile I got several text messages. One of these messages confirmed which plan I had activated. I really appreciated this.

I did not have to restart my phone to have the data and service work, but I restarted it anyway because it is no major hassle.

After I did all this I checked my Straight Talk account and my phone was disconnected from Straight Talk’s service. I had 1GB out of 2GB left, I lost this, but I would have lost this at the end of the week anyway when my month of Straight Talk was over.

This will save me $269 a year, accounting for taxes.

I only ran into one snag and I think it's something Mint Mobile needs to be aware some users may not be able to get around. Once my purchase was made and everything went though, the app asked me to make a password for my account, I'm sure this is the last step of the process. The app would crash as soon as I started to type in the second box, the box that says confirm your password. I tried everything to get around the crash including typing in the second box first. Finally I went to mintmobile.com on my laptop and had the website send me a temporary password (this feature worked great and saved me a call to your support team). I then restarted my phone and tried the app on my phone again and I got the same screen that asked me to create a password. The app continued to crash at the same point. I reinstalled the app and signed in and everything works great. This create a password hiccup took 20 minutes (not a big time investment at all!)

One other thing is that the $5 cost of trial comes out of the cost if you activate a plan. Last I checked I have a pending charge on my credit card for the cost without the $5 deducted from the bill. We will see if the discount is actually charged to me.

The other thing still in question is how easy it will be to move from the iphone 5c to iphone Xr by moving the Mint Mobile sim card into the new phone?

Feel free to ask me questions if anything isn't clear or I skipped over anything. I'm also wondering if my experience is common so please let me know in the comments!

Edit: One other observation. I’ve never had Wifi calling in the past. When I activated Wifi calling the carrier tag at the top left of my phone changed from “Mint” to “T-mobile” and changed back when I flipped off wifi calling.