The Campling process of MS is as follows for roaming Ms
1. It will scan for the HOME PLMN network,that is the network he is registered on.
2. If not able to get the signal then it will look for the NCC which has been permitted by the Service operator,,,,and this list is stored in SIM Card itself.
3. If it finds then camping occurs otherwise.
4. It scans all of the avialable PLMN and camps on the PLMn which is best suited in terms of Signal strength
Thats all