I checked that link and my phone doesn't look like the phone on that page. For start, my phone slides 'sideways' like real N900 should and not up-down like phone on that picture. Second, that phone has 0.3MP camera, mine camera is better than that. Also, that phone supports 2 sim cards and mine supports only one. There are probably more differences but these 3 i mentioned are moste obvious. As far as I know we don't have official Nokia store here in Serbia. I bought the phone from authorized dealer who was listed on Nokia web site. I also checked my IMEI number ot this website http://www.numberingplans.com/?page=analysis&sub=imeinr and it turned out that my IMEI should be real Nokia number for N900 phone.
I am planning to contact seller tomorrow and see if they can help me. Anyway, thanks four your time guys (especially yours x61), if you have any more ideas I'd be happy to hear them.