After activating iPhone 4 with no SIM card, can I use any SIM card ?

Mo Kanjz said:

If I unlocked my iPhone 4 with no sim card using greenpoison, can I use any sim card I want to (even if not US?) .... Nd let's say I bought it 200$ with contract, can I not pay monthly at all, send the phone out of the country for my friend and can he use his country's sim if unlocked that way ??

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I think you can do that. But instead of that unlocking method let me suggest you a proper permanent unlock service. I suggest you can approach Theunlockarena.com and specify the country,locked network of iPhone 4.Based on the availability you can get the permanent unlock service along with free instructions.