Not all texting stories are free. Some are, but many come with costs like ads or limited access without paying. You need to check the specific app or website to know for sure.
A girl I knew got a text from her ex - boyfriend who had passed away a year before. The text just said 'I miss you'. She thought it was some cruel prank at first. But then more texts came. 'Why did you forget me?' She was really scared. She showed the texts to her family, but they thought she was making it up. She changed her number in the end, but she still wonders if it was really her ex - boyfriend somehow reaching out from the other side.
You can start a texting story by introducing the main character and their situation. For example, 'John was sitting in a boring meeting when his phone buzzed. He saw a text from an unknown number.'