The police report actually says she was arrested for having the phone out in class, disobeying the teacher, and lying to the School Resource Officer (guy who makes sure there's no drugs, shootings, etc.) and principal; texting had nothing to do with the actual arrest. They had witnesses who said she had the phone out and after they searched her, they confirmed that it was used to send a text message to her dad. The girl was apparently a troublemaker and gave the officer several fake phone numbers instead of her parents'.

Why would you need a warrant? She was arrested on disorderly conduct and frisked. Unless something has changed recently, it's standard procedure to frisk the person you're arresting.

The finglonger, but that was never actually invented. The Professor was just watching it on the What If Machine.