Mobile Phone at the Airport
Can I RENT a mobile phone to be used in Switzerland and Germany at GVA airport?
I don't know of any place to rent a phone. But you might be able to buy a cheap one at the airport. There are at least two shop that sell phones at the airport.
I'm not sure how their prices are. If you take the train into Geneva there is a shopping centre at the train station where you arrive - lower level. I'm sure a shop there would have a phone.