RE s-pen work with other roms: probably -- I have put a "KK1" rom on and the S-pen and apps still seem fine. KK1 rom is some rom from HongKong and is an 'official samsung rom' (er, based on full samsung rom but some stuff removed.
RE: polish NOTES only? No i don't think so -- the OP of this thread appears to have a german NOTE. However there is at least one other guy on XDA with a polish NOTE from negri with same problem. There are a few people on XDA that have had similar issues but gnotes from different places. Their 'recipes' for fixing have not worked for me yet.
RE: re-seating the sim: countless times. I have cleaned it too. I have inserted it in to a N1 and a SGT -- both work. It is a very old SIM - but it is a 3g one. I guess there is a very remote chance that my "gnote lost its taste for it"?
RE: sim lock or sim change no or not on purpose -- but i will double check that...actually I am not aware of the sim change feature. I have heard about sim lock feature, but never used it. Please feel free to elaboborate on either of these...
Finally -- still stuck with a gnote what works well except for the phone and data part (wifi still works well). More details about this can be found here:
[Q] SIM not detected?? (ATT + polish GNOTE) - xda-developers