how do i unlock my iphone 3gs for free

Where did you get it, and where did it originate?

You have to speak with your carrier.

If it is an AT&T phone it is not going to be unlocked for free ao for any charge. Period. If it is another carriers phone check with the carrier as to their policy regarding unlocking.

ONLY the carrier the phone is locked to can authorize unlocking. Most carriers charge a fee for this and have conditions regarding being a current customer, paid in full and having had service for a minimum time period.

I have tried to get AT&T to unlock my 3GS and failed so far, but there is definitely a way to do this through Apple. You need to somehow get the attention of Mr. Tim Cook, President of Apple, Inc. If you succeed, then he may intercede with AT&T on your behalf. No guarantees it will work for you, but it did work for one (1) guy according to news reports.