Memorizing phone numbers

Hiro is chatting with an attractive girl on the platform. She asks for his telephone number but he can’t recall it.

...

Mimi: What’s your phone number?

Hiro: My phone number? Aw heck, I can never remember my phone number.

Mimi: Never mind.

Hiro: Hey, wait.

Mimi: Too late. The train’s going.

...