If she has detailed billing, she'll be able to tell the numbers to which you are texting. She won't be able to read your texts but you should be aware that the City of Detroit was found to have a right to the texts sent by then-Mayor Kwame Kilpatrick and his Chief of Staff, Christine Beatty. They had perjured themselves in a trial and texted about it. They both went to jail (although everyone in Detroit found reading the details of their affair more interesting when the texts were published in THE DETROIT FREE PRESS). My point is this: Everything you text is a digital record at T-Mobile. If you were later involved in a crime or something, the text messages could be subpoenaed. I doubt it would happen, but do be cautious what you put in text. It's a permanent record.