question

Technically, yes, you could use a custom game server that we host, and which you use to arrange the matches between players. But I believe what you're asking is, can you go a turn-based multiplayer game without using Photon, an external data table, or custom game servers - would that be correct?

It would be possible to create a fairly limited version of turn-based multiplayer using a combination of leaderboards and our data systems, but it's really not advisable. A robust multiplayer matchmaker needs to keep track of the game sessions that are available and manage players joining them to keep things working smoothly. For that, and specifically for turn-based multiplayer games, we would recommend using Photon for the matchmaking. The billing for Photon is based on concurrent user peak for the month (CCU), and the common estimations for MAU->DAU->CCU are usually 10x per step, meaning that most games would need to have around 10,000 MAU before they would be over 100 CCU at peak (which would be $19 a month at the current rates). Given the amount of work you'd need to do to work around this, and the potential issues, I'd strongly recommend going that route, as it'll be a significant net savings in the long run.