If your iPhone is running stock 3.1.3 at this time you will NOT be able to jailbreak your iPhone to enable internet tethering.
The only way this can be done is, if your phone was jailbroken previously and you have a SHSH file on server that would enable you to downgrade your phone to redo the jailbreak.
But if your phone is new, or it was never jailbroken. There is NO current jailbreak for 3.1.3.
The only way this can be done is, if your phone was jailbroken previously and you have a SHSH file on server that would enable you to downgrade your phone to redo the jailbreak.
But if your phone is new, or it was never jailbroken. There is NO current jailbreak for 3.1.3.