How to transfer all my contacts onto my sim card?

I got a new phone and i want to transfer all my contacts on to my sim card so i can put my sim card in my new phone, how can i do thins? My old phone is an iphone 3gs

I'm afraid you can't. Iphone 3gs can only import from sim to phone- Your other way is through a PC- connect to Itunes. Selct your device's name at the left handside under devices. Then go to info at the top select> Sync contacts, make it> to windows contacts. At the bottom right> click on sync. Done ( or else: googlemail can be anotehr option-outlook… )

If you have a mac, repeat the same, but insead of windos contacs it could be i contacts, or else

P.S: always select merge as sync is always both ways for contacs, never put replace as it will replace ones on your phone