I bought a BB Bold 9900, supposedly unlocked, yet when I put in different SIM it connects to the network for a second and then it disconnects, yet it works fine on Rogers. Took it to the mall and was told it's corporate phone, it is unlocked but still works only on rogers.. guy suggested I flash the phone.. what did he mean? What can I do to unlock it now?

I unlocked a few 9900 and I just buy code online, put in different SIM and it asks me for unlock code.