Sim card activation - Cell Phones

1. Remove the SIM card or have it with you.
2. Write down the numbers that are printed on the SIM card. ...
3. Contact your wireless provider to activate your SIM card. ...
4. Give the IMEI number and SIM card number to your customer service agent.
5. Put the SIM card into your phone..

Borrow your friends sim card or if it's an older iPhone try using redsn0w to hackavate the phone

You don't. There's no way to do that without paying for it. Sim cards are the direct connect to the company. The company has to allow a sim card to use it's services...
You can't "hack" a sim card for free anything.

Ask the SIM CARD dealer that your Card activated/deactivate when you purchase it. After clear that insert your sim card and wait for computer response.ie. New Divice found... Now got to control panel and select Network setting. Change them if it is not ready to use... thanks

Buy the new sim card from network operator shop.. they will give you the New sim and activate it

Well, first off, an iPhone won't work at all with a T-Mobile SIM card. American iPhones are locked to AT&T's network -- only AT&T SIM cards will work in them.

As far as activating it with AT&T, make sure that the iPhone isn't connected to the computer while you install iTunes. Once iTunes is installed, connect the iPhone to the computer and iTunes should launch automatically and begin the activation wizard. Just follow the instructions on the screen and answer the questions.