So please forgive the complicated circumstances here. I'll try to break down the individual bits. I am an Australian travelling Europe using the OneSimCard travel sim. I was in a public hotspot using FaceTime (over Wi-Fi, obviously) with my iPhone 4S, and it suddenly cut out. I tried to text the people I was chatting with but discovered that somehow it had drained my last $40 of credit. I was definitely in Wi-Fi because obviously the FaceTime wouldn't be available otherwise. It didn't click with me what happened and I just recharged it with credit using the Wi-Fi access as I'd need it for my trip anyway. FaceTime then worked again. However, when I later checked the sim card balance I had been slugged with 38MB and 58MB transactions and my new credit balance was down another $60. $100 on data in the space of fifteen minutes. It seems damn near impossible to me since I am very careful to only use 3G when absolute necessary. Is it possible that the sim card/billing system could think that because I'm "calling" a contact it needs to charge for it? Is there a reason why FaceTime is being deducted as data even when in wifi? The support desk at OneSimCard told me that "your phone can not determine using one connection over the other if both GPRS & WI-FI options are enabled in this case the phone was using GPRS as well." They also said a background process (Photo Stream, auto downloads or something) could be responsible. I'm pretty sure that's rubbish as I know the iPhone prioritises Wi-Fi over cellular for exactly this reason and if I can be having a FaceTime chat all that background traffic would also be on Wi-Fi. They're basically alleging: 1. FaceTime was initiated in a wi-fi hotspot. 2. Simultaneously, and despite being in wi-fi, and contrary to the iPhone's programming that prioritises wi-fi over 3G, a rogue background process during the call did an automatic update or something and downloaded 37MB worth of cellular data. 3. The sim's credit is used up, and coincidentally the face-time call ends. 4. I check the credit and am able to refill it on the website recharge page because I am still in wi-fi. 5. Once credit is returned I am able to resume FaceTime over wi-fi at which point I then also resume downloading 58MB of data but over the air instead and apparently in the background. The fact that I could recharge my phone credit at all indicates there was nothing wrong with the Wi-Fi. Never mind the fact that I apparently downloaded the 58MB in just three minutes according to the bill, which is blisteringly fast for cellular data (and probably better than the adsl I get at home)! Is there something I'm overlooking? I had a friend who said that last year he discovered Telstra (Aus carrier) had mistakenly charged him for FaceTime data so I believe that it can happen. Has anyone heard similar, and have any advice?