To Victor:
It is mandatory that the UE shall search for its last Registered PLMN in every supported bands at power on(UMTS2100, EGSM900, GSM1800 and possibly even GSM850 and GSM1900 depending on the implementation) before possibly reselecting a different PLMN, such as a National Roaming Partner. Today, such a scan takes a long time in dense or complex radio environment, which means the UE can spend over a minute!!!!! searching/synchronising/decoding cells where only Foreign PLMNs are to be found.
Hence your problem is overall Mobile system problem, not Nokia 2G BSS one.