The player can only start obtaining the Gym Leaders' phone numbers after entering the Hall of Fame. Most numbers can only be obtained on a certain day of the week and/or at a certain time, and some have additional specific requirements. Most of the Gym Leaders give out their numbers personally at a location outside of their Gym; the two exceptions are Chuck and Blue, whose numbers are received from their wife and sister respectively.
The following table shows when, where, and how each Gym Leader's number can be obtained:
↑Lt. Surge will not appear while Zapdos is present.
Rematch schedule
The following table shows when the Gym Leaders are free to accept a rematch. Once the player have acquired a Gym Leader's phone number and all 16 Badges, they can call a Gym Leader during their available time slot and challenges them to a rematch, they will show up to the Fighting Dojo and wait for the player. They will remain there (even after their available time slot has ended) until defeated. A Gym Leader can be defeated and then called again repeatedly within their available time slot for multiple rematches.
If the player does not have all 16 Badges they will simply be told that there are "stronger trainers out there for them to challenge" by the Gym Leader they call, even if it is the right time slot.
As midnight to 3:59 AM is considered to be "night" by the game, any Gym Leader whose available time slot is at night can be called for a rematch from either midnight to 3:59 AM or from 8:00 PM to 11:59 PM.