How do I unlock an Iphone 1G?

My friend gave me an old Iphone 1g. I have a t-mobile SIM Card which I would like to use on the iphone. I inserted it and I receive text messages, it reads t-mobile at the top left hand corner and it accepted my SIM Card password. The only problem is, I can't get into the phone itself. On the home screen, if I slide the 'slide' key, it sends to me to an emergency call rather than unlocking the phone. What do I do? How do I unlock it so I'm able to access the phone? Also, itunes recognizes the iphone but it gives no information about it and says "the SIM Card inserted in this Iphone cannot be supported."
 
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