Type of Phone: IPhone 5s
IMessages worked on Sprint just fine
Post Mint Activation
The Mint Rep told me, did you read the small print?
yada, yada, yada...
Sorry you have to be on WiFi for the 5s to work iMessages, really??
Don't jump the gun yet.
My research found a recent article dated Jan 15th 2019.
The person that wrote the Article is someone that travels a lot and flips SIM's in and out like a poker game at Vegas.
He reported, since IOS-7, IPhones have had issues (A Bug) with iMessages and FaceTime, because they lose their brains on SIM swaps
His Very 1st Step "Power Cycle" Phone...
I remembered I had not restarted the Phone after the Activation was completed.
Silly me, I should know better, since I say that a hundred times a day to others.
Ok, I went one step further.
Knowing an IPhone Power Cycle is more like a Hibernate related to some IPhone Features like iMessages and Face Time, a Hard Reset was called for.
I Went with a full Hard Reset....
iPhone 6S and earlier, iPad, and iPod Touch: Power button + home button
iPhone 7 and 7 Plus: Power button + volume-down button
iPhone 8, 8+, and X: Volume up, then volume down, then power button
Press & Hold the specific buttons for the phone in question and when the screen goes off and the Apple symbol shows back up, release both.
It seems like the Hard Reset tells everything to reread what it is, who it is, and who's network it's on.....
After that one step my iMessages now work