Let’s be honest, a mobile phone with internet is an absolute must! As soon as you arrive you will want to get organised.
Now, my experience was that I couldn’t get a Swiss sim card without presenting a residence address. If you are staying in the temporary address like I was, I gave that address and it worked for me.
I know of three mobile networks; these are Swisscom, Sunrise and Salt. I chose Salt because it was the cheapest pay as you go. The network coverage has been excellent. Again, I went to the shop, took a ticket number (they love those here in Geneva) and waited for my turn. Here, I was lucky because the lady spoke English, hurray! ☺ The formality was to fill out the form with my home address, passport (for the photocopy) and then I could choose a pay as you go package, plus internet and my new phone number. Internet costs me 1CHF per day. Pretty straight forward, no mishaps there!
To recharge my phone with credit, I either log in online to my account, use the app or buy it directly from the phone shop.