3310 with 1800MHz but no 900MHz?

Hi, I have a 3310 which has brilliant reception on 1800MHz (Orange and TMobile), but no reception at all on 900MHz (Voda and O2).

The phone has not had any hardwre trouble ever... when I do a manual network search, I do get all four networks showing!

What's wrong? I need to use voda on my 3310!

could it be a blocked IMEI? I don't think so.. (i bought the phone second hand).

Is it possible to block the IMEI of a phone from one network/frequency, but left unblock on another? As that is the only explanation I can think of.

hmmm interesting...