UPDATE: I FOUND A FIX
The following are instructions that I added modifications to for clarity. The original instructions were found at XDA at https://forum.xda-developers.com/galaxy-note-9/help/sprint-calling-plus-t3832684
I should also note that these instructions DO NOT activate Calling Plus per se. After completing these instructions you will NOT see an option to activate Calling Plus in the settings as usual with the Note 8. Instead, you can simply place a call and use data. No function to activate. It just works - like it should. In fact, I'm using it right now. (WARNING: I HAVE NO IDEA HOW THIS WILL AFFECT THE SPRINT BILL! YOU'VE BEEN WARNED).
1 - Download Shortcut Master (LITE)
2 - Open it and click "Search" under the menu and searched for enhancedlte
3 - Click the option that pops up (should say "Mobile Networks
com.samsung.blahblahblah.EnhancedLteServices)
4 - Click the Launch Button from the 3 boxes that pop up. (If an advertisement shows after doing this, simply hit the back button on the bottom navigation bar.)
5 - Check the box for "Enhanced LTE Services"
6 - Hit theBack button on the bottom navigation bar.
7 - Search for LTEFunctionality
8 - Click on the top option (Should say com.test.LTEfunctionality
com.test.LTEfunctionality.LTEfunctionalityTEST)
9 - Click Launch from the 3 boxes
10 - Scroll down to VoLTE Test UI and click it
11 - Turn on N/W PS voice support and N/W PS E911 support
12 - Hit the back button on the bottom navigation bar.
13 - Exit the App.
NOTE: I restarted my phone after doing this but I don't think its necessary. It should work after completing the above steps.
OMGGG your instructions worked flawlessly.
I just got mine yesterday and was quite irate that it didn't have the calling plus feature like the S8 and s8+. Thank you so much.