RORY: Paris, how did you get this number?
PARIS: Oh, relax. I won’t call you on Prince William’s precious phone again.
Prince William (born 1982), member of the British royal family, and since birth, second in the line of succession to the British throne. In 2002, Prince William was enrolled at the University of St Andrews in Scotland, and considered one of the most eligible young bachelors in the world. (By the next year, he was dating fellow student Catherine Middleton, who would eventually become his wife).
Paris never says how she got Dean’s cell phone number. Presumably she had a snoop at Rory’s pager some time.