How do I get texting to work on a Verizon Samsung Galaxy S4 with T-Mobile service?

I just got this phone about a month ago and I am not able to send any text messages but yet, I can receive them. MMS, data, and calling works pretty good too. MMS didn't work at first until I had to change my APN settings. Is there a way to fix this?

Does this problem have something to do with the software version? It's 5.0.1 (lollipop)