If it's mainly just for receiving calls, pre-pay is probably indeed the way to go.

About which operator: I suspect that when it comes to pre-pay, all of them are about the same.

Nir

Thanks Nir,

Where could I buy them? Do you know of a place near the train station?

Yallo do a really good deal, for prepay they are the cheapest... i had it as an au pair and it lasted me a long time... just be careful, should you go below 50cts credit, you cannot be reached nor can you call out...

Here's an idea I use......go to a large Migros, one with an electronics department, "M-Electronic" and you can buy a M-Budget SIM card for 19.90, which includes 15 Francs of calling credit. You have to register this SIM in the store BEFORE you can use it, and this requires ID (work permit or passport), name and address etc. No idea why, but it's the rules.( I bought one on a Saturday, got home and had to wait until Monday before going back and registering it). You are then set up in a few minutes. M-Budget uses the Swisscom network, so good to go for all of CH. I think you can top these up, but haven't tried yet. Calls in CH and Europe are only 10cts per  min, which is cheap.

Prepay: Lebara - can be bought in many shops and topped up over the web. Pros: Cheap. Offers huge discount when topping up a large amount. Cons: Expensive data roaming, 41 CHF/MB.

International and data usage: www.Transatel.fr. Speaks English. International roaming rates are local rates in five countries. Subscription only.

It's worth to note that an unused, even activated, prepay SIM will expire if not used in a period of 9 months (may vary).