SkankPhone is a part of Apple's internal debug utilities suite. It can be defined as a SpringBoard alternative. Instead of dividing the iPhone OS functions such as Phone, Safari etc. into standalone applications, Apple developers combined many functionalities into one app. SkankPhone has a integrated phone, web browser, music player and SMS editor. Pressing Home Button reveals a toolbar with 5 shortcuts to other SP sections: Phone, Web, SMS, Music and Setup. In Alpine 1A420 prototype firmware it also had a built-in Operator screen.
SkankPhone can coexist with SpringBoard. When the SkankPhone.app is linked into /Applications/SkankPhone.app, it shows up in SB and can be launched (if you have 1.x firmware). During launch, SkankPhone kills SpringBoard.
SkankPhone does not depend on SpringBoard, SkankPhone can live with or without it. It is not like a regular UIKit application, in this way, it is not linked with UIKit and uses it's own custom framework. SkankPhone's framework located in it's application bundle named SkankKit, this is small UIKit replacement. SkankPhone is launched by a daemon. Somewhere in this process SkankPhone unloads SpringBoard's daemon, this kills SpringBoard while giving SpringBoard no way to respawn.