Several points have to be taken into consideration before jailbreaking an phone. Such points include things like the OS in use, backups and applications to be used after breaking among others. Here are some steps that may be used to jailbreak iPhone for Sprint.
For an iPhone 3G for sprint, first download the application Redsn0w 0.9.9b7 for windows. This application can then be saved on the desktop in a separate folder. This way it would be easy to access the application when you require it.
The next thing is getting i0s5 file for you device. Extract the redsn0w zip file to the folder which is already present on your computer. Now connect the phone to the computer. This is enables by either a USB cable or via the Bluetooth.
If your phone is upgraded, go to the redsn0w folder and double click on this application. Note that for windows XP and windows 7 users, this application should be run as Administrator. Also it should be noted that other operating systems would require you to manually follow a couple of steps.
After clicking on the jailbreak button a prompt will appear requesting you to plug in your phone and switch off the computer. By following the instructions, click onto the next button and later turn the mobile phone to UDF mode where redsn0w will guide you through several steps.
Your phone will reboot and redsn0w will prepare the necessary jail breaking data. A prompt appears requesting you to choose several options where you will choose Cydia. The phone reboots again and uploads the new RAM disk and kernel. On completion click upon the finish button where the phone reboots for the last time and the jail breaking process becomes successful. The cydia applications would now appear on your gadget.