How do you get Mary and oaks number on Pokemon Heart Gold?

You can't get Mary and Oak's number in Pokemon Heart Gold. There's no feature in the game to obtain phone numbers of characters.

Here's why:

* Limited Phone Functionality: In Heart Gold, the only person you can call is your rival. The phone is primarily used for progressing the story and receiving important information.

* No Social Interaction Focus: The game doesn't focus on building social relationships with characters beyond the core storyline.

* Game Design Choice: The developers chose to focus on the core Pokemon gameplay experience, and adding phone numbers wouldn't have contributed significantly to that.

If you're hoping to connect with Mary and Oak, you'll have to do so within the game's storyline and interactions.