contray to the above post i book a taxi via calling in and book it to arrive for 7.30 am sun-thursday and they are always on time, the only gripe i have is you can only book 2 days ahead, which can be a pain if you forget to pre book and as for hailing i cab, i have got one from various locations in doha, and rule is stand somewhere they can safely pull over and they will ! again never had a problem nor waited longer than 5-10 mins,oh and watch out for the indians who are touting illegally, they have no insurance and if you get caught, it is a thousand riyal fine (these are usually white cars) the legal ones are turgoise and all the drivers are knowledable and chatty,