SDK - Software Development Kit. The set of tools supplied by Apple that allow developers to access the inner workings of the iPhone and create third-party applications.
SIM - Subscriber Identity Module: A removable smart card which stores security information identifying subscribers on the network.
SMS - Short Message Service: A collection of capabilities that allow users to transmit and receive data messages of a limited size across two endpoints of a cellular network, one or both of which may be a mobile subscriber. Short messages are transmitted within a cellular network and are encoded based on defined standards. SMS allows the ability to 'mobile originate' and 'mobile terminate' from a cellular phone. SMS is also known as "text messaging" and "texting".
Springboard - The iPhone's stock software that runs your home screen from which you launch all applications.
SSH - SSH is a command line program that allows you to remotely establish a secure connection between your computer and your iPhone. Using SSH, you can access the iPhone's file system from your computer and securely transfer and alter files.