In the pilot, after having sex for the first time, Greg takes a shower while Dharma lies in bed. Greg's mobile phone, in his pants pocket, rings. Dharma reaches over and answers the phone.
Dharma: "Greg's pants. He's not in them right now. Can I take a message?" *beat* "This is his wife, who's this?" *beat* "Oh hello, Gregory's mother."
- (Also pretty awesome, as it's a joke that probably couldn't have been used even a few years earlier.)