Hi opencube,
Welcome to the forum, I'm new here too, but am in your situation, et me share my experiances...
First off, a short sweet answer to your question, if you debrand and update your software:
YOU WILL LOSE ALL YOUR FREE 3 STUFF
I know this to my cost :)
I have an
n95-2 (the 8gb one) also on 3. Because of the various problems I had, and after gleaning info from this forum I decided to update my software (which as you know on 3 is limited to v11.0.0.26) . So I de-branded my phone and run an update, SUCCESS! I updated to v15.0.0.015. But oh know!!!!!
In my haste, I didn't do a backup (stupid!!) and I found that after the update, the most important service (the 3 Launcher Application) was gone! The activation key for the Spiderman 3 Movie was also gone (understandably) and all the 3 pre-installed apps.
I have been in contact with 3 over this, and they are of no help (Be warned). The most reasonable advise I got (over like 6 calls to 3) was that if I take my handset to a nokia care center they can roll back to v11.0.0.26 for me.
I do plan to do this, BACK UP the 3 launcher application (btw, no-one at 3 seems to understand what this is!) and keys and stuff, and do another update to v15 then restore my 3 Launcher App.
I will keep you up to date as to how it goes at the Care Center....