Hello, I bought a Samsung, model GT-I5500, with Android 2.1-update1. After installing the SIM card, when trying to make a call, the phone displays the message "Not registered on network". The icon indicators section displays the message "Selected network unavailable". I have tested the same SIM card in another phone and it works fine. The signal strength of cell network is strong also (-81 dBM according to the GT-I5500 phone). Thanks in advance.