The star of (gone-but-never-forgotten) 'The Simple Life' may soon say good-bye to the single life.

Paris Hilton marked a milestone birthday last week, turning 30 with boyfriend Cy Waits at her side. And when she called in to chat with Ryan Seacrest on her big day, she confided (to all Seacrest's listeners) that she was "sure" Waits would propose to her. "We love each other very much," she said, adding with a giggle, "We'll see what happens."

Engagement rumors escalated Friday when Hilton and Waits were spotted in a luxury jewelry store in Manhattan. A source tells, "They shopped for engagement rings....They were really cute together. Paris was making comments about the rings, and joking that her ring has to be at least 24 carats."

While there's been no confirmation of an engagement-related purchase, Waits allegedly bought her a $25,000 "white gold and black diamond" ring, a gift which Hilton's rep has since called "something special for Paris' 30th birthday."

Bling wasn't the only gift Waits gave Hilton: The big-spender boyfriend also bought her a new white Lexus. "It's so sick," marveled Hilton, while chatting about the car on Seacrest's show.