Hmmm, this is really strange mate...

I'm starting to think that you probably need another firmware.
So do you know if it probalby needs another firmware variant?
like:
Maemo 5 USA release for Nokia N900
Maemo 5 Middle East and North Africa release for Nokia N900
Maemo 5 India release for Nokia N900
Maemo 5 UK release for Nokia N900

Or another idea would be trying another simcard, or ask your provider for a new one.

Last thing that comes to my mind is:
do you get the loading animation? the dots? If so how patient have you been? Because the very first boot after flashing could at least take a few (minutes) seconds...

Sorry, for not being able to help you more...

Regards,

J4ZZ