Microsoft’s final build of Windows Phone 7.5 includes a mobile hotspot feature.
Internet Sharing (ICS) is included in the RTM build of Windows Phone 7.5 and appears to require carrier activation. The feature was discovered by WPCentral who note that it’s present in the settings menu for Windows Phone 7.5 build 7720.68. The data sharing feature will allow Windows Phone 7.5 users to share their cellular data connection over Wi-Fi with up to 5 guests.
Early reports suggest the feature works well but impacts battery life in a significant way. The device (shown below) is an AT&T Samsung Focus. Despite the discovery, Microsoft has made no official mention of the hotspot data sharing feature. The company is launching the first Windows Phone 7.5 device in Japan today and is expected to reveal more devices next week.

Windows Phone 7.5 mobile hotspot