Jailbreak is a term used in iPhone models. Samsung mobile models doesn't require a jailbreak. What is the exact problem with your Samsung Galaxy S?
You won't be having any problem in adding third party apps for a Samsung Galaxy S. If at all you are not able to add third party apps, It must be a problem with your anti virus protection. Turn off privacy to add third party apps. Or if you need to unlock your Samsung Mythic from network restriction, You need to enter it's unique unlock code.I m afraid you cant get this model unlocked for free but You can get affordable unlock code from any vendors online like WickedUnlock.com