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I used Full Circle Wireless when I sold my iPhone 3g to get the iPhone 4 on launch day. I had a 8 gig 3G and they paid me $160 for it. I did go through the commitment process a couple of weeks before launch day, packed it up and sent it to them a coupl eof days after I got my iPhone 4 and got it to them just in time to keep the higher price, then it was a full 30 days afer they got my phone before I got my check, but it was a pretty good price for a phone I paid $200 for two years earlier.

http://www.fullcirclewireless.com/
 
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