The default text message tone on iPhone is Note. While using custom message tone on iPhone needs some tricks, you can change message tone on iPhone 6 and other iPhone devices, using available text tones, by doing as follows:
1. Open the Settings application
2. Go to the Sounds settings
3. Scroll down to Sounds and Vibration Patterns settings, and tap the Text Tone option
4. Mark the message sound you want and you are all done.
** Note that, if you set to Alert Tones to None, the there won't be any sound when receiving a text message. It goes silent.