@applee Oh, that makes sense. I appreciate your help trying to figure it out.
The Nexus 5 is supposed to have the capability to support WiFi calls and texts, but if UT doesn't support it and MMS won't work, and the signal keeps dropping and is poor quality, I guess I'm stuck. I tried making a call today and the quality was awful and it kept dropping due to the signal.
I could possibly make it still work if I had a good app that could do voice and video calls, but none of the apps currently have that capability yet.
Thankfully Mint Mobile has a 7 day return policy so I can cancel it and get my money back.
I guess I'm stuck with AT&T for now which really sucks.. AT&T sent me a notification saying they are going to be changing something and they won't support older phones (even my Android phone) next year, and none of the phones I have are on their list of acceptable devices.
Anyways, thank you @AppLee and everyone who replied