I know the prepaid service on Lycamobile is what most people use if they are using a Swiss number to call their family and friends to the US, I do believe it's the cheapest, but I talk way longer than I can afford those dang 'top up' cards.
http://www.lycamobile.ch/rates.aspx?lang=EN
Alternatively, I still have a US credit card/bank account so I just bought a Vonage where I pay 30 bucks a month and get to call to most countries (I call between US and India which works out best for me)
I'd say think about how long and who you are going to call, sometimes, because of the move, most of your friends and family will Skype you when you are home and Skype to Skype is free (if you are thinking about getting the internet as well).