We usually throw sim card when it gets expired / unregistered. This may also lead to environment pollution like other electronic equipments does.
Never throw an expired or unregistered simcard. The sim cards available in India comes with 64 k or 120k memory( k means kilobytes). Even if it cannot detect the service providers network. Its memory can be used to save your precious contact numbers, because every now and then smart phones are stolen and the common grievance is the loss of all contact numbers.
Just insert your old expired sim card in any latest phone that you use and then you can copy all contacts from the phones memory to the simcard memory.
This way you can create a chip set of different contact numbers saved in different sim cards and then you can keep it safe somewhere in you cup board.