Hello everyone,

Would it be possible to update US's model to european firmware after purchasing? Would that be legal?

Since the warranty is worldwide accepted, then I don't see why I should buy the European model?(yes I live in Europe)

Thanks in advance.

If Nokia does the same thing as with their S60 phones, which I doubt, you can change the product code to get the firmware for that region.
I think Maemo will have an universal firmware for the whole world since it's the same phone (with keyboard differences?) throughout the world.

Does this mean that, if I buy from Germany or UK, the warranty is valid in Bulgaria?

Warranty is NOT worldwide. It never is.
However, it is somewhat unified in the EU. If bought in a EU country, the N900 is under warranty for 2 years everywhere in the EU. If i remember it right, it's only 1 year in USA and may not be applicable outside it (otherwise americans could just have it repaired in europe in the 2nd year).
As for flashing: you don't sign anything when you buy, so you can put whatever you want (if it works) on your device. It's yours. It may possibly void warranty, but i seriously doubt that. And if the images used are freely available, you can flash whichever you want

It´ll be applicable in Europe for us in the US if we buy it in the EU and send it back for repairs. I sent my N95 from NC to Denmark once for warranty service, actually on the very last day of my 2 year warranty.

It was promptly repaired under warranty and was with me 10 days after I sent it.

It seems like the firmware isn't just the OS. The OS is the same for the whole world, but regarding the preproduction units, Nokia said that some lower parts of the firmware need to be flashed, too, in order to make them more equal to production units.
I have no idea what these lower parts are about, but I suspect this is where region-specific stuff like the allowed strengths of the radios are defined, or where the FM transmitter can be disabled for certain regions.

And remember that wi-fi channels regulations / availability are different around the world... channel 12-13 for europe or 14 for japan for example.
(and power emission is/was different)