Will t-mobile charge me for making phone calls using google voice?

I just installed the google voice app on my iphone. I live in TN and my friend lives in TX, I wonder if I'm going to be charged by t-mobile for making a long distance call with google voice app.|||If you are using Google Voice, you aren't actually using your phone plan, you are actually using the data/internet. If it is all in the United States, it should be free.