When I add people to my mobile telephone book, I am asked whether I want to save to SIM. Does this mean the number doesn't go in the memory of the SIM card?
If you save to your SIM card, it means the numbers will remain on the SIM card so you'll be able to keep your numbers if you put it into another phone. If you save to your phone, it means it will only be stored to the phone's memory.
BUT, if you save to phone, you will be able to insert a photo of the caller (if you have one or if you intend using one later). That way, when you receive their call, you will be able to identify there pic, rather then tring to read the text, usefull if you are of a certain age.