How do I import all contacts from a SIM-card to an Android phone?
Two questions:


Are you sure the SIM contacts were really imported or only displayed. 
Is the option to show phone contacts checked after you changed the SIM.


If you go to Contacts, press Menu -> Import/Export -> Import from SIM card.

The SIM contacts should be imported into the phone and remain there. It is then just a matter of getting phone contacts displayed.