You have to search Johto and Kanto and find all the gym leaders out side of there gyms and and then talk to them and they will eventually give you their numbers
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
it was about two or three of the gym leaders
Find them on a certain day, time, and place and you will get their phone numbers. Then, on another certain day/time/place you can call them for a rematch.
After you defeat all 16 gym leaders, you can call them to arrange a rematch through pokegear in fighting dojo in saffron city(kanto). See related link below to get gym leaders phone numbers and when to call them.
You need to get their Phone Numbers, by taking a picture with them at certain times of the week, and time zone. there is also a place where they will go after you get said phone number reference youtube for dates/times for the rematchs.
think its 99
Erika- Saturdays & Sundays 3-5 pm.
Gold phone numbers are for separating pay as you go numbers and pay by contract numbers. Gold phone number are customizable and personal to you and your business.
america
You need to talk to the man standing outside the day care centre
Blackthorn and mohogany
at their gyms.....