If you have followed the last few blogs of Jailbreaking IPhone, then the only thing required to do is follow the steps below.
1. Connect your IPhone to a Wifi Network
2. Update Cydia, if its already updated Ignore this step . Cydia gets installed as part of Jailbreaking.
3. Open Cydia from Iphone and click the search button
4. Search for ultrasn0w and install the software
5. Restart your Iphone and put in your SIM , you will get a message that your SIM has been activated. Thats it you have successfully unlocked your Iphone 3g