The last names for the characters Kelly Taylor and Justin Bell, played by Kelly Clarkson and Justin Guarini, come from (respectively) their stepfather and father.
When the girls are leaving the beach, Alexa gets the first text message from Justin. They show her phone up close, and you can see her phone has no antenna. When she puts her phone back in her purse, the phone has an antenna.
During the dance sequence for "That's the Way (I Like It)" Kelly's shoes change twice. At the beginning, she is wearing open-toed black shoes, which turn to sneakers for about two seconds, then back to open-toed shoes. At the end, she's wearing sneakers.
Kelly finds out that Alexa has been texting Justin, and walks away without her purse. In the next scene, Kelly starts singing "Anytime," while walking and carrying her purse.