Why do our cell phones have sim cards?

why did they switch to sim cards when they worked without them?

Why do our cell phones have sim cards?
hehe. If you have a SIM card then u are on a GSM network (cingular, T-Mobile, etc.). Sim cards Rock because you can easily switch between phones. Unlike old TDMA phones where you had to get your phone all reprogrammed if you lost it, broke it, or replaced it.
Reply:It makes it much easier to move internal directory information to a new phone. The information gets stored in a memory chip anyway, and the makers concluded that making the chip movable would be a good idea. They were right.
Reply:bec it stores the contacts and all the ring tones and so forth
Reply:I think it's because when people want to get a new phone or switch to another phone, they can have all their contacts available on the sim card and just use it on the other phone. It makes it a lot easier than having to re-add everyone again.
Reply:only some phones have sims cards. like cingular. sims cards are used to store memory. so lets say you save some phone numbers pics and stuff in ur phone, and u broke ur phone, well they can remove the sim card put it in another phone and all ur stuff is there.
Reply:They enjoy being difficult, Big Brother is watching.