How to get a sim card in Geneva, Switzerland?

I'm a student moving to Geneva soon. I already have an iPhone and want to get a sim card/swiss cell phone number.

You select the provider you want, go to its shop and take along some official ID and then buy the SIM card

You can go to Balexert is a shopping center or other places that are near you there's a shop that has available sim card(lebara) with perfect offer you only pay about 10chf but you have sim card and about 30 chf charge, isn't it perfect?