Now that Windows Phone 8.1 Preview for Developers is available, I was looking forward to testing out Cortana. However, it's initially available only in the US. For those outside the US, it doesn't seem to show up anywhere and the search button still launches the standard Bing app. The settings page can be reached by searching for "Cortana", but the option to enable the feature is greyed out and says "Not available in this region".
My question is, what exactly is checked to determine whether or not Cortana is available on a particular phone? Tom Warren says on Twitter that setting the phone's country/region to the US should suffice, but in my experience that's not the case, Cortana is still disabled (see screenshot below). Is something else checked for, like other region/language settings? Or the currently active mobile network? Or the region of the Microsoft account that the phone is connected to?