If you intend to jailbreak iPhone 4 then you need to have the right
software application to do exactly that. There are many software
applications online, this means that finding one wouldn't be an issue to
many individuals. However, you do not want to be among the harrowing
statistics of jailbreak went wrong iPhone users. The fact of the matter
is that it is not as easy to find a reliable software provider as we
would like to believe. You will need to be cautious enough and get a
provider who has received sufficient positive feedback from others.
sources:
4.1 Jailbreak
IOS 4.1 Jailbreak
IOS 4.3 Jailbreak