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.
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.
When Kelly gave Justin her phone number, she used an area code from Texas (972) which is where they are all from. But when Alexa later gave Justin a phone number for Kelly she gave her own cell phone number. She used the area code 239 which is actually in Florida.