Security issue with unlocking my iPhone 4?

I'm not sure if anyone here will be able to help me but I am trying to get my iPhone unlocked with AT&T. I bought my iPhone on contract through AT&T in December 2010. My account is in good standing. I paid my ETF, it's technically eligible to be unlocked. I called AT&T on April 9th for an unlock and it's now April 19th and still no wordd from them. I've called several times and they won't tell me what's going on other than that "there is a security issue with unlocking my iPhone and the issue is with Apple, but they are working on it." From my understanding, all AT&T needs is the unlock code to enter into the system and unlock it from there. I don't know what security issues could possibly exist that would create a problem. The only thing I can think of is that when I orginally bought my iPhone it turned out to be a lemon and had to get it replaced the day after I bought it. I did this through an Apple store since it was around Christmas. The IMEI number on my phone doesn't match the one AT&T has on file, but that shouldn't matter? I gave them the right IMEI number that is on my current phone. Does anyone know what "security issues" can exist when it comes to unlocking an iPhone 4?