You can get network phone code for sony ericsson t303 from Mobile-unlocker.com
Here Are SOME Advantages & Disadvantages...
Advantages:-
-Access more stuff on your device like themes etc.
-Download paid apps for free easily
Disadvantages:-
-MAY slow device
-Your device warranty goes
Although people say it's iligal, it's not.
When you download apps you don't download them from Apple's app store, your downloading from cidia there for making no copyright/illegal clams
"Jailbreak" is a term coined for removing the limitations on Apple-made products. Removing the limitations of an Android device is called rooting.
1.) Download and install a program called "SuperOneClick" to your computer. Once installed, open the program.
2.) Dismount the SD card, connect the phone to the computer via USB cable, and enable USB Debugging Mode (Go to Settings > Applications > Development USB Debugging. Click to enable.
3.) Click Root to root the phone. The program will say OK when it finishes. Check to see if Superuser shows up in your apps. If it does, you have successfully rooted your phone.
DISCLAIMER: Rooting a phone can damage the phone and WILL void all warranties the phone has. Do so with caution. Neither Answers.com nor I claim any liability for damages created before, during or after rooting of a device. These steps are provided for informational purposes only.