The main languages spoken are Dzongka and English.
The local currency is the Ngultrum (equal to Indian Rupee). Credit cards are generally accepted at hotels. There no ATM's in the entire country of Bhutan.
To call internationally from Bhutan, dial: 00 + country code + area code + telephone number. Hotel receptionists will help you make calls.
Only global cell phones will work and only in the bigger towns. You may want to consider renting one or getting a satellite phone.