There's a Swisscom shop at Zürich airport but it seems like the "Natel Easy BeFree" tariff has been replaced by "Natel easy smart":
NATEL® easy smart: Mobile Prepaid SIM Card | Swisscom
With the new "easy smart" tariff data will be billed with just CHF 2 per day but bandwidth is throttled to 1 MBit/s down/0.5 MBit/s up from the beginning and will be further reduced after exceeding 2GB.