You have it right, debranding is overwriting the networks firmware (Rogers) with factory firmware. You need 3 files. MAIN, FS, and Custom. The Custom file is the file that the networks change (brand).

You can do it for free using a few pieces of software, I recommend XS++ because thats what I have used, and can tell you that it worked with my Fido/Rogers branded phone.

You can do it yourself, and for free, as long as you can find the appropriate files for you phone. You can download most here, but need to be a Premium User (2 euros or wait a month with 20 posts), or you can search the net.

The phone will still be locked to Rogers, so you cannot use a different carriers sim card with it, but I understand that you just want to debrand so you can use MP3's as ringtones.

XS++ 1.6.7 will work with CID 49, 51 & 52. You need the usb cable that came with your phone (DCU-60). Will also need the SEUS drivers, these are made by Sony. Download the SUES application from there website and install. If using Vista it will install the drivers for you automatically when you connect your phone when its off while holding the 'c' button.

First run XS++ to find out what CID and firmware version you have, so you can search for the correct files. You might as well update the firmware while you are doing this if its available. You may need to update to CID 52 if yours is 51, but if you can find files for 51 then use them.

Its pretty safe to flash these phones, most problems can be recovered.

hope i answered everything for you, but if not just ask.

good luck