For those who have a valid code and could not unlock the phone. i found this great article, it worked for me.
http://dudoanketqua.com/Unlock_HP_Ip...structions.htm
I belive he offers unlocking codes for those who don't have them.
All i had to do is flash the ROM with the official one from t-mobile/HP. the version seemed to be the same as the one i already have, but flashing the ROM fixed it.

Problem i'm facing with the unlocking.
Any reset including a soft reset removes the unlock status and i have to unlock it again, not a big issue since it only take 10 seconds. but it would be great to get rid of that problem.

A Problem I am facing in the new ROM that didn't exist in the old one. I can send files to my 6315 by right clicking the file, clicking on send to then choose my documents on PDA.
But when i try to explore files, it shows up empty. so i can no longer treat my PDA like a folder and drag files into it.