iPhone won't work without an AT&T Sim Card! HELP!

I can't even get to the Home Screen without putting in a AT & T Sim Card can someone help! It says "No Sim Card Installed, Insert a valid Sim Card without a pinlock to activate iPhone" (I want to run the iPhone with T-Mobile..)

Also, I'm in desperate need of finding a Unlock for the iPhone 3g 4.2.1 that allows me to update via iTunes when I need too. I don't want the hassle of always updating through pwnage tool. Link me to YouTube videos if possible!

EDIT: Do you think buying this would get me to the home screen because right now I can't even go to my home screen without a AT&T sim. I was thinking of buying this:

http://cgi.ebay.com/ws/eBayISAPI.dl...277732&ssPageName=STRK:MEWAX:IT#ht_5224wt_907

Please Help!

labman said:

There is no unlock for 4.2.1 you are sol for now sorry but it's more about the baseband then the firmware I am guessing you didn't preserve baseband and updated via iTunes. If so all you can do is wait.

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Okay. But do you think buying this would get me to the home screen because right now I can't even go to my home screen without a AT&T sim. I was thinking of buying this:

http://cgi.ebay.com/ws/eBayISAPI.dl...277732&ssPageName=STRK:MEWAX:IT#ht_5224wt_907

chrishemley823 said:

This. Pwnage Tool 4.2 activates iPhone.

Click to expand...

Can you explain?? I have PWNAGETOOL 4.1.3 on my computer. I just checked the "About" in the programs.

So what exactly what do I have to do?