Sim lock and Phone lock issues

[llzt2004]

About a 6 months ago my phone suddenly had a sim lock issue. The woman at apple I talked with had no idea why this started locking on it's own. It just sometimes locks. Well, trusting her, I set up a 4 digit pin code (and i know the pin code because it is a very familiar number to me) and have been using this same code every three to four days to unlock my phone because it mysteriously locked. Today, my 4 digit code was/is not working. It locked me out many of times. I called apple and (after initially sending me back to att) they said that there was no way my pin would have changed. They refused to help me without charging me because I did not purchase apple care. They said in order to give me the code I would be charged. The apple tech told me I could research the answer online. so I tried doing things that were suggested on forums in this site and I have now managed to disable my iPhone and the sim code problem is still not fixed. I can not hook my phone up to my computer because I hooked it up on my work last and my profile is cleared every time i log out so it will not recognize it. It also will not recognize it at home because it was not the last place i had plugged it in. If anyone can help me find a solution to get my hone up and running again I would appreciate the help. Or if you know how much apple charges that would be helpful also.