Jailbreak and unlock are two different things.
You can jailbreak any version phone on any version firmware especially a 3G.
There are several options available to Windoze users for jailbreaking right now. The most reliable is to find a friend with a Mac and have them make you a custom restore IPSW or download a trusted one from the Internet
https://forums.macrumors.com/threads/803052/. You can then install the IPSW on your computer using iTunes. Or there is Blackra1n, but I can't recommend it although others will.
As I told you earlier, there is no unlock for Baseband 5.11.xx now and none expected in the foreseeable future.