Since texting directly from the tablet isn't supported on Sprint, you'd need an app that connects and syncs your phone to the tablet (but bear in mind the phone has to be on and connected to a mobile network or WiFi if it supports WiFi Calling for the messaging to work). My favorite is Pulse (since it has an app for pretty much any platform) or Migthy Text (this one has a monthly limit if you don't choose the quite pricey subscription). Google's Messages is free, but doesn't have an app for the tablet so you'd have to use the web interface.