Hi sfrazier9999! By default T-Mobile does not have any device that has push to talk. I do not see them adding this.
However there are apps on Android and iPhone that will work for this. Keep in mind these apps are not supported by T-Mobile. I have personally tried the TiKL app and love it.
Here are a few apps that will allow for push to talk
HeyTell
iPhone Android Windows
TiKL
iPhone Android
Voxer
iPhone Android
iPPT
Only iPhone
Let me know if this helps
Nevin