it was about two or three of the gym leaders
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
america
Blackthorn and mohogany
at their gyms.....
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 can't
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.
In HeathGold/SoulSilver the leaders will be the same from Gold/Silver and Crystal. This means the 8 leader from Johto and the leaders from Kanto, one for each type.
your able to pick a kanto starter
no sorry i wish only johto and kanto
you cant get to sinnoh in heart gold, but you can find the gym leaders from sinnoh.