Received today( via Martin Lewis) thought it may be of help to some. QUOTE.. A new iPhone setting could eat into your data allowance, as when you think you're using Wi-Fi it may automatically switch you to your phone's data. This could land you with huge bills or being cut off from using the web if you don't have an unlimited internet data package. The problem could affect ANYONE who has upgraded to the new iOS 9 operating system, even if you don't have the new iPhone 6s or iPhone 6s Plus. The new feature in question is called 'Wi-Fi Assist' which the settings clearly state will "automatically use mobile data when Wi-Fi connectivity is poor". If you have iOS 9 and do nothing, the default setting is that this function is switched on. While Apple hasn't returned our calls to confirm this, on the many devices we tested it on, this was the default every time. This will use your data allowance much quicker than you may expect, and in the extreme, could mean you have to pay for extra data if you end up above your limit and want to continue using more. Vodafone, for example, allows you to continue using it at £6.50 per 500MB. But worse would happen abroad where extra data can cost up to £8/MB. The problem could affect ANYONE who has upgraded to the new iOS 9 operating system, even if you don't have the new iPhone 6s or iPhone 6s Plus.