There are at least hundred of small guest houses in this building and you can always find a vacant room. All of rooms are very small, but considering the location (which is perfect) and price, it worth to stay here.
I stayed in Singh Guest House which I booked online, and there was no window in the room. Although, there was no gsm signal.
Later I stayed in the different guesthouse in the same building (Chungking Mansion, you can easily find it near Tsim Sha Tsui station) and I had both a window and gsm signal in the room. Although, the staff and service was better in Singhs Guest House.
Haggle to get better price!) Most of guesthouses owners are from Asia.More