Tripadvisors "Instant booking" feature is currently available only in 11 countries:
US, U.K., Australia, Canada, India, Ireland, Malaysia, New Zealand, Philippines, Singapore and South Africa.
Hotels from all around the world can set up "Instant booking". The country restriction regarding this TripAdvisor product concerns the guests - the "Instant booking" feature is only available to guests booking from the above mentioned countries. If guests book from any other country, the "Instant booking" "Book Now" button will not appear to them.
According to tripadvisor a global rollout is expected in the first half of 2016. http://ir.tripadvisor.com/releasedetail.cfm?releaseid=953277