Antenna Amplifier??

[zipur]

Is there such a device? As I understand it the Wifi Antenna is on the back I was wondering if there is a stick on-Kinda-External Antenna which you could connect to extend the range of you wifi or Cell signal. I used one on a PC at a remote maintenance shop a few weeks ago and I was surprised how much gain it provide. Like this (although this is for a PC) these are about eight inches long.
http://www.dandsuppliers.com/product_images/p/756/images_prodLarge_HAI7SIP__36883_std.jpg