Gear Diary stumbled upon a SIM Card attachment that will unlock your iPhone 3G by piggybacking onto your current SIM. This hardware-based method of unlocking fools the phone into thinking it’s a special “test mode” SIM, thus allowing any GSM carrier to access your iPhone 3G. To boot, it won’t void your warranty since it’s a removable hardware method. iPhone acting up and you need to take it to the Genius Bar? Remove the attachment and take your phone in.

If this were the very first iPhone, you’d expect to pay around $100 for this kind of accessory. At DealXtreme, you’ll pay $17 for the freedom to use any GSM cellular provider you desire.

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