You must search in various places. I have 2 gym leaders phone numbers, Clair and Sabrina. Clair's in dragons den on fridays and Sabrina's at the Fast ship S.S. aqua dock on saturdays.
Go to serebii.net and click on heartgold/soulsilver. click on gym leaders.
Yes.
you beat them in a battle
No, you don't. You cannot face the Sinnoh Gym Leaders in HeartGold.
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
In the Trainer's House after getting their phone numbers.
Call the gym leaders on the pokegear once you get their numbers and go to seribii.net to find out when and where you can find them.
18
no.
defeat all the other gym leaders
Beat 16 Gym Leaders.