How to unlock iphone 4s for free without buying anything?

So it can be used with other cell phone companies.

Not possible.
you carrier can do it if you off a 2 year contract with it.
otherwise you will need to pay.

Jailbreak it? But you may ruin your phone and it's a risk but only you can decide if its worth it. Google 'Jailbreak iPhone'

If you've completed the contract with your carrier, they'll unlock your phone for free. If not, you can always get it factory unlocked but it will cost you money. You can mail this person (arghyle@rocketmail.com) who can help you get the phone factory unlocked.

You can't unlock your Iphone 4S for free. But you can unlock it at low cost. Use remote unlocking service to unlock your Iphone 4S. Get the service from the site http://www.superunlockcodes.com/apple-iphone-4s/rs12wp9/ and unlock it yourself using unlocking instructions.