Shared Extension is when a group of agents has one and the same extension line. During the incoming call the phone will ring at several agents simultaneously.
Mirrored Extensions is when you have one and the same extension line on several phones, in example, in the office, at home and on the cell phone. So when someone calls your extension all you phone sets sharing the same extension will ring.
MobiGater is a device which transfers your Skype calls to your mobile phone without the use of SkypeOut credits. It connects to your cell phone via a SIM card placed inside it, and using a USB cable to your PC and Skype.