Before Installation, please make sure of the following items:
A) Your iOS device has been jailbroken.
B) Your WiFi has been enabled.
C) OSCall source has been added into your Cydia.
D) SIM Card has been installed on OSCall device.

How to jailbreak your iOS device?
There are many websites that teaches how to jailbreak your iOS device, some examples include:
http://www.idownloadblog.com/jailbreak/
http://www.iphonehacks.com/jailbreak_iphone

How to add OSCall source into your Cydia?
Connect via Wi-Fi after your iOS device has been jailbroken, and then open Cydia->user->Manage->Sources->Edit->Add.
Appearing under the url, enter "http://www.boenz.com/c" and click
Add Source.

Installation of SIM Card
Insert your SIM Card into the OSCall SIM Card Slot on the side of the device as illustrated.