I'm using my old SIM card, where all my important numbers are stored, with my new Android. The problem is that the device seems to totally ignore the contact details saved on the SIM card and displays them as "unknown".
How to import my SIM contacts?
Open the Phone App > Contacts.
Press and hold the Menu button.
Tap on Import/Export.
Select "Import from SIM card".
You can either save the contacts to your Phone or your Google account.
The list of contacts present on the SIM will be displayed.
Press and hold the Menu button, select "Copy to phone".