From the Super Mario Wiki
Mobile Golf is a Mario Golf game that was only released in Japan. In terms of gameplay and storyline, it is very similar to Mario Golf on the Game Boy Color. A Mobile Adapter GB could be used to play multiplayer games within a mobile phone network.
Like Mario Golf, it has four human characters to choose from at the beginning. They must be trained in the same fashion by playing golf in an RPG manner and gain experience. Players are also given the ability to unlock characters as well by beating them, such as the four champions of the game: Bean, Rozary, Powert and Bird.
Several human characters from Mario Golf (Game Boy Color) can also be unlocked and played in story mode. Mario characters unlock that can be connected to using a mobile phone network, unlockables include Mario, Peach, Yoshi and Foreman Spike. Service using the Mobile Adapter GB has ended.
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