To add more characters to your team, tap on the "Base" icon at the bottom of your screen, and then tap on “Radio for Characters”.

From the Character calling screen, you can call a single call character with 1 Walkie-Talkie Radio or 300 Diamonds. You can also call ten characters at once with either 10 Walkie-Talkie Radios or 2700 Diamonds.

Once an Ultra Character has been promoted to its maximum rarity it will no longer be available in Radio Calls, to make collecting the rest of the Ultra characters easier.