Nokia 6225 / PM6225

My son and daughter in law both recently bought Nokia 6225 phones and are on the same network as my wife and I who both have Samsung SCH-N181 phones. We have recently been away in the country with them and whilst in most areas both our phones were able to pick up the network and use the phones, neither Nokia 6225 phones would pick up the network and receive or make calls. Any other Nokia 6225 users have similar problems? We live in Sydney, Australia.