Guests arriving at the Aloft Hotel in Manhattan or one in Silicon Valley will soon be able to do something hotels have dreamed about offering for years: walk past the check-in desk and enter their rooms by using a smartphone as a room key. The boutique hotel brand from Starwood Hotels & Resorts Worldwide plans to offer this feature at two hotels, in the Harlem neighborhood and in Cupertino, Calif., before the end of the quarter. Guests at these properties will receive a message on a Starwood app containing a virtual key, which will unlock the door with a tap or twist of their phone through the use of Bluetooth technology. The company says the iPhone 4s or newer models and the Android phones running 4.3 or newer will be compatible. Starwood officials are hoping this will be one of the biggest technological changes in the industry since free Wi-Fi.