It's not a game, it's an experience.
Mobile devices have some unique features that set's them apart from other game platforms.
- Mobile (O RLY?) The user carry the device around so game sessions can be short as a subway ride and can be spread out all over a day.
- Position The phone game provide a position and support games where location matter.
- Touch They are touch based and no one cares about buttons. Some phones have buttons but if you depend on them your market shrink to nothing.
Mobile Operating Systems
The OS that matter is iOS and Android.
A lot of devices use this and far to many to test them all so have fun developing for it. Touch screen but have some buttons that your program also need to support.