The smartphone is a more advanced version of a regular cell phone.
Role on Night Watch Island
Gus, the former night watchman, left a smartphone in an Quake-Master in the MacGuffins store at the Twin Palms Mall. You will eventually find the cell phone, and you use it throughout the entire quest of Night Watch Island.
The first app is a security camera. With this app, you can monitor all 12 rooms in the Mall.
The contacts list is a complete collection of all of the contacts on the smartphone. In addition, this is where you call other people, like owners and Gus.
The notes app is pretty self-explanatory; it is used to take notes when necessary.
Planet Slug is a minigame that is similiar to the popular real-world game Angry Birds. You do not have to play it, but it is fun to play.