I have a chinese phone/gps tracker. It works perfectly around Hamilton on 2degrees, but won't roam on vodafone out of the city. When I insert a vodafone sim, it just says ' invalid sim, failed to register' A network search gives me the option of 53024 (2degress) and Vodafone NZ, and if I select Vodafone NZ it shows signal bars OK. It's as though the phone has locked on to 2degrees only because that was the only signal it used for the first three weeks.

Any help appreciated.