iphone 4 6.1.3 jailbreaking

Ok, there is this iphone 4, 6.1.3, its locked to some Japanese network.
I want to jailbreak this thing to what ever the latest stable jailbreak is available.
Is it possible? and which software do I have to use?
/not sure about Sho’s new username
Answer #1
Download redsn0w from here
http://www.redsn0w.us/2010/03/download-direct-links-jailbreak-guides.html
Then follow the instructions in the software…
You should have a ‘tethered’ jailbreak, the final step should be to ‘just boot’ (or boot now, something along those lines)
When you ‘Just Boot’, you’ll need another software called P0sixpwn from here
http://posixspwndownload.com/
That should allow you to install a ‘full/proper’ (untethered) jailbreak.
NOTE – I wouldn’t suggest updating to iOS 7 on an iPhone 4, it’ll be quite laggy and would be a hell of a battery drainer.
Answer #2
Thanks, will update
Answer #3
LMFAO!
I said….
I wouldn't suggest updating to iOS 7 on an iPhone 4
Answer #4
I meant will update the thread
Turns out its already jail broken iphone, but cant make phone calls with it. Not sure whats going on.
Answer #5
As its ‘Locked to some Japanese network’ it obviously won’t work anywhere other than Japan…
It needs to be unlocked either from the original carrier in Japan or from online (some people offer these services), whether to trust them or not is up to you to research
Answer #6
Thanks Adil, will take it to some shop that does this.