Hey guys, today i will show you how to jailbreak/unlock IOS 6.1.3 iphone 3gs (old bootrom).
Before we start let me tell you that i have done this only on 3gs old bootrom NOT NEW BOOTROM.

Requirements:
1. Itunes
2. Snowbreeze 2.9.14
3. stock IOS 6.1.3
4. redsnow
5. stock IOS 6.0
6. iexplorer

Before you begin you have to see to it that you currently are on an IOS below 6.1, in case if you are above 6.1, then restore your iphone to 4.1 ios.

Instructions:

step 1: download the above tools, then run snowbreeze. in snowbreeze select 6.1.3 ipsw that you downloaded from above. it will ask for bootrom select old bootrom and when it ask for activation click yes. now wait for your custom 6.1.3 prejailbroken firmware to build. (Ihope you have some patience bcoz it takes some time).

step 2: Once your custom firmware is built you will see it on the desktop by the name "sn0wbreeze_iPhone_3GS-6.1.3-10B329_oldbootrom". now put your iphone in recovery mode NOT IN DFU MODE, and restore the custom firmware that you have build.

step 3: After restore your iphone will be on activation screen, you might be thinking that you had activated it in snowbreeze so why is it asking for activation? dont worry iexplorer is on the rescue. install iexplorer (download link is provided above). run iexplorer, under your iphone details click files, under files click root. double click applications folder, in applications folder, you will find setup named folder, delete that folder. after deleting setup reboot your iphone. after reboot your iphone will be activated and you can see cydia.

step 4: In the previous step you can see that your iphone is jailbroken. now time to unlock. run redsnow (if on windows 7 run as admin), click extras, slect ipsw, select 6.0 ios, then come back click jailbreak, deselect install cydia, select downgrade ipad baseband click next and complete the procedure.

step 5: once downgrade of ipad baseband is complete, open cydia >> manage >> sources, add a repo "repo666.ultrasn0w.com" and install ultrasnow. After installing ultrasnow restart springboard and then put sim and check, it will show you network after some time.

Now you have untethered jailboken/unlocked 6.1.3 iphone 3gs.