Originally Posted by Schizophonic
Can he wipe it clean (not unlock) and put an OEM Blackberry OS?
There is not an OEM OS, per se. For example, the Bold OS 22.214.171.1247 released by AT&T is the same as OS 126.96.36.1997 released by Rogers (not sure if they actually released that version or not, but it's just for example). You can install any carrier's "official" OS onto any other carrier's device, but it takes a couple of steps during installation to make it happen. Nothing difficult, but it isn't as simple as install and go.
As Midnightdraven indicated, however, there is no way to remove the carrier branding from the startup routine of the device. You can, however, install aftermarket themes that eliminate certain carrier elements found throughout the device (but that still doesn't change the startup image branded by the carrier).
Additionally, with a bit more work, you can even install any carrier's custom theme onto another carrier's device if you wish. This is a bit more difficult than installing the OS, but it is still very possible to do.
So, the short answer is that your friend should just install a theme that is carrier non-specific to remove as much of the carrier branding as possible, bearing in mind that the phone will still have some branding to it. You can find plenty of themes that look and behave just like the stock themes but that have no carrier designation to them.
Hope that helps.