I don't think you can....
You can, but all you have to do is go to the Kanto region and find a trainer named Billy,school boy,he on route 15 beat him and he'll ask to exchange numbers click "yes" after that he'll tell you where the gym leaders hang out when they're not in respective gyms...
that's when you could battle them for rematches...
Chat with our AI personalities
All of them have phone numbers, but there are certain ways to get them. I would try looking up "how to get all gym leader's phone numbers in heartgold" on google
he will be anwhere see him and you get his phone number when you talk to him
After you defeat her, you will automatically register her in the Pokegear.
There are a variety of things you can do. You can get Janine's phone number in the Mt. Silver entrance. You can also go to the top of Mt. Silver and battle Red.
you can go really early in the morning to get her phone number and rematch her again