Actually most older phones (first generation gsm-phones) stored sms (and contact-list) directly on the sim-card. Swapping the sim into another phone and you wo

Actually most older phones (first generation gsm-phones) stored sms (and contact-list) directly on the sim-card. Swapping the sim into another phone and you would have everything accessible. Some phones had their own memory also so you could choose where to store it or it would revert to SIM when phone memory was out. Problem was that the memory on the SIM was incredibly slow and small and had no support for advanced contact list management(like multiple numbers per name), so now every phone has its own storage.