chances are that the routers are on channels wifi 12-14 and nokia doesn't support them.
Had the same problem and found no fix. On linux normally you can change the country region for the wifi driver (rt2500 for example) with iwpriv wlan0 set CountryRegion=6
This depends on the driver though and n770/n800 driver doesn't support region changes.

It seems however that if you check with 'iwlist wlan0 freq' you will get all channels, so it seems the limitation is from a higher level, probably the connection manager.

cheers