Usability 
Marriott's mobile webapp covers all of the company's hotel brands; Marriott , JW Marriott , Renaissance, Courtyard, Residence Inn, Fairfield Inn, TownePlace Suites and SpringHill Suites. And it's international, you can check availability and book rooms in 58 countries.
Other features of Marriott Mobile include online access to your Rewards account, basic driving directions and information of Airport Buses and Taxis, including approximate fares.
Phone numbers are in click-to-call format and the site shows live room availability with prices and allows you to book a room. Booking does require a credit card and all the hassle that entails. But if you are a Marriott Rewards online member and have a saved credit card on file with Marriott you can zip right through the booking process by just entering your Rewards number and online password - nice. One thing I'd like to see that's missing though is a click to call number right on the booking page so that non-members can complete their booking by phone.