Are your friends telling you they can't hear you, but you can hear them? Check and make sure you've allowed Textfree access to your microphone.
To enable access to your microphone:
1. Go to your device settings, by tapping on the settings icon
2. Scroll down until you see Privacy
3. Within your privacy settings, scroll until you see Microphone
4. You'll now see a list of apps which have previously asked for your permission to access the microphone
5. Make sure Textfree is turned on. It will be green if you have allowed access