Best pre-pay mobile plan for visiting family? (smartphone)

Sorry if this has been covered anywhere, but I couldn't find it. Has anyone recently investigated the best deal for short-term visitors to Switzerland (max 30 days)? Swisscom has some data packages but you need to be a Natel "subscriber" and it appears there's an auto-billng feature, rather than a true, pay-as-you-go plan.

Any thoughts appreciated. FWIW, this would be for an iPhone 5 or 6, and call and text aren't nearly as important as cheap data.

Thanks.

Best pre-pay mobile plan for visiting family? (smartphone)