well, first of all you'd better to watch W2AEW's awesome video about Decibels to actually understand what you're doin'.
here's the antenna I've bought (the seller told me it's 18cm high but it's 19.5cm ):
and this is the SMA connector, before you buy the connector, you have to find out if your antenna's connector is male or female. in my case it was male so I bought a female connector for it:
then you have to solder some wires to your antenna, one for the ground and another for the signal. coaxial cable is the best solution because of lower noise but it's so thick, here is some antenna wires I just found with a quick search on Ebay, and they're not that thick. also keep wires as short as possible, in my case I just wanted to test the antenna so didn't care about the wires:
the two connectors above the camera on the back of the phone are for WiFi, and the two below the SD Card are for GSM. so I connected the wires of antenna to the bottom ones, and, here's the result:
with the original antenna (which is the cover door of the phone):
without any antennas (without cover door):
with the external antenna:
I'm planning to drill a hole on a cheap cover door and mount the antenna on the cover, and also add some more antennas like GPS and WiFi. (then probably it won't fit in any pocket )
if you tried it too, please hit the thanks button.