Jailbreaking iOS mean you are releasing your iDevice from Apple's Chain and now you are free to downlad and install applications which are restricted by the Apple in iOS. Jailbreaking has pros and cons, you must read this before you make any decision:
http://www.mobilefun.pk/mobile-phone-news/ios-jailbreaking-pros-and-cons_103.html (http://www.mobilefun.pk/mobile-phone-news/ios-jailbreaking-pros-and-cons_103.html)
http://www.squidoo.com/what-is-ios-jailbreaking (http://www.squidoo.com/what-is-ios-jailbreaking)
Yes but in pakistan it is very common it has not so much harm or damages