@1040
Actually OK Mobile did not only change their tariffs with the introduction of the "22/15" tariff in November 2011 but they also switched their supplier. While the
original OK mobile prepaid SIM was based directly on Orange Switzerland's network their
new "22/15" SIM is based on the MVNO "Talk Easy". Talk Easy also use the Orange network but run their own billing platform and customer care. This means you cannot switch from the old to the new tariff as the SIMs come from two different companies despite using the same network. In any case Orange is the worst network in Switzerland as its current owner France Telecom had been trying to get rid off it for quite a while and in the meantime has neglected the network so it lacks EDGE support and 3G performance is also subpar. Orange was finally sold to the British investment company Apax two weeks ago.
Depending on how long you stay and much data volume you need I'd recommend either a
Swisscom Natel Easy BeFree SIM which gives you unlimited internet access at CHF 4.00/day or a
Sunrise go dayflat SIM for which there's the "Sunrise surf" option giving you 250MB for CHF 7.50/month or a Lebara SIM (also using the Sunrise network)
offering 150MB for CHF 4.90/month and quite cheap international calls (e.g. Netherlands for CHF 0.19/min with the
Lebara Simply tariff)