I'm not sure about this 100% because I don't have original configuration screenshots, but it seems that after upgrading the OS from 4.5.0.127 to 4.5.0.169 my BB 8830 unlocked itself. All items below are now shown as "disabled", and as far I remember, before the upgrade, Network was shown as Active (the device was locked):

How do I determine if my BlackBerry is "unlocked"? - BlackBerryFAQ

The original OS was the official OS from Bell Mobility and 4.5.0.169 is from US Cellular. I have never come across this unlocking trick mentioned anywhere.

Upgrading can't lock or unlock a BlackBerry.

I thought so as well, but I even had this on my To-Do list, to call Bell and ask for the unlock code. Seems strange, I'll leave it at that, no complaints, new OS works great, too.