Swisscom has sent a minor automatic change to all their mobile customers. The IPHONE or HTC new automatic connects to their Swisscom WIFI Hotspot if in range (Stores/Malls/Airport).
Because you handy is connected to WIFI it may think you are HOME or in the OFFICE where you may have unlimited bandwidth access.
In most applications/Apps you can tell the IPHONE when and OVER what connection to UPDATE. In this case the IPHONE
is connected to WIFI and think it's at home and does larger updates.
The transfer size will clearly swap over the limit of 250MB/500MB/1000MB you have with Swisscom and thus for any fuirther MB you pay.
In the report from SFDRS is a short movie how to turn this off.
http://www.srf.ch/konsum/themen/multimedia/mobile-eapsim-swisscom-trickst-kunden-aus
http://www.id.uzh.ch/dl/mobil/wlan/CheckSSID/iphoneEAPSIM.html
http://www.fhnw.ch/services/ict/email/smartphone/deaktivierung-eapsim_iphone
Please make sure you turn off this option of you are a Swisscom mobile customer.