Thank you, Quantumrand!
I have started a thread on Google Mobile Help to outline my specific issue, some more users with the same problem replied, but no reaction from Google - I am not sure they are even aware of it, let alone they are trying to solve it... I feel like I am "rolling back"to my good old SE P910i (6,5 yrs old, indeed and still kicking), I will at least be able to make/receive the calls and SMS... So much for the Android, used it for 6 months...
My baseband version seems to be I9020XXKI1, do you think the same GB installation file should be applicable as for the I9020T or I9023?