B-Mobile has recently slashed down the tariff of mobile Internet access (see announcement here). It has also added an "unlimited data" postpaid package for Nu 999/month. This is a terrific deal, and I won't be surprised if this is the cheapest unlimited 3G package in the world.
Remember that the Bhutan Telecom broadband plans (DSL) do not include "unlimited data" plans. So if you're using fixed-line broadband and consuming more than 5GB or so of data per month, it might make sense for you to switch to 3G. This will also add the capability of being able to use the Internet away from your office or home. There are a number of caveats, however: The initial price of the cellular modem is high (around Nu 5000); you will only get 3G-speed in Thimphu (in other Dzongkhags the speed will be slower); and the connection is technically harder to share if you have multiple computers in the office, although it is doable.