have an iphone 4 officially unlocked
i have an iphone that is from canda and officially unlocked. i just want to get understand well about jailbreaking the iphone. when you jailbreak the iphone you did that to download free apps right? and can i do that with the officially unlocked device or is there any way i can download cydia or installer without jailbreak.
and i heard that it opens some ports for the iphone if jailbreak the iphone and it easy from hackers to get to my iphone.