Phones approved by the FCC are seldom so upfront about the OS they run on, but HTC decided to go against the status quo in its latest filing to the government agency. A quick perusal of the FCC filings show a handset tested for 850 / 1900 GSM -- standard 2G bands for AT&T and T-Mobile -- and no WCDMA frequencies in the US. There's one detail in the docs, however, that stands out like a sore thumb: this device, the HTC PI39110, is listed as a Windows Phone. What's more, the paperwork also mentions the inclusion of a "WiFi hotspot," which likely is the mobile hotspot feature confirmed to be supported by Mango. HTC hasn't announced any devices that run on the updated OS yet, but this particular gem could very well be the long-rumored Eternity. While it probably won't make its way to the US, this is at least a solid indicator that Windows Phone 7.5 is coming soon to more parts of the globe.