By Private Taxi
A more expensive option than bus, taking a private taxi from Phnom Penh to Banlung is possible, for about US$120. It's a 5-6 hour drive to the junction near Stung Treng, then 2-4 hours to Banlung, plus meal breaks. Some taxi drivers in Phnom Penh specialize in this trip. Your hotel/guesthouse will probably be able to help you out.
Vietnam
The border crossing O Yadaw Cambodia to Pleiku Gia Lai Province and Quy Nhon Viet Nam has been opened to foreign travellers. Vietnam visas are not available at the border but Cambodia visas are. From Pleiku town, take a public van 2 hours or taxi 1 hour and 30 min to the border. The Cambodia post is isolated with no regular transport. The immigration police may help find a taxi; bargain - up to $80 for a whole car or $30 for a motorbike with driver. 70 km; 2 1/2 hours. Highway #78 has been completed and is now one of the the best roads in Cambodia.
By bus
Road Conditions:The road between Phnom Penh and Stung Treng has recently been upgraded and sealed though a newly reconstructed road south of Kratie through Chhlong is more often used as it saves 100km and can be negotiated rather quickly. The road between the Stung Treng junction and Banlung is mostly unsealed but is currently 2012 being rebuilt, including a long diversion around the proposed Lower Sesan 2 hydro dam.
It is possible to get buses to Banlung from/to:
Phnom Penh - Doing this in a single day is now reliable, with 4 'big' buses Sorya, Rithmony, Hy Long, GST; R39,000/$9.70 and numerous minivans R40,000/$10 servicing the route regularly, departing from 6 - 7:30am. The minivans are faster but the free pickup and dropoff can add 2-3 hours to the 8 hour trip.
Kratie - Two options currently 2012-04:
Shared minibus. Leaves around 8am, takes 5-6 hours. Costs $8. Beware that they seat 4 people in each row of 3 seats, so it can be packed.
Phnom Penh Soraya Transport (http://www.ppsoryatranspo...) bus. Leaves 12:30pm. Takes 5-7 hours. Costs $8. Buses are often late.
Stung Treng - 3-5 hours, later departures.
Laos- It is possible to buy a ticket to Four Thousand Islands in Laos from Banlung. These are not direct buses; you must take three buses, switching at Stung Treng and at the border, and then a boat to your final destination. Costs $14-18. Despite what you may be told at the Lao Embassy in Phnom Penh, Laos visas have been available on arrival at the border since about October 2009.
By plane
Banlung has an airfield within the town, but all commercial airlines have stopped servicing Ratanakiri. The only flights were with Mission Aviation Fellowship, in an 8 seater, but these stopped at the end of 2009. Medivacs and charters are available from Helicopters Cambodia.
At Phnom Penh Airport a US$6 departure tax may be levied. Currently the Ban Lung runway is still a gravel strip, but there are plans to extend it and build a concrete runway, which would make it more likely to attract a new carrier and make cancellations in the wet season less frequent.