Phonsavan's Xiang Khouang Airport (XKH IATA) has 4 flights per week to Vientiane.
Lao Airlines offers six flights a week in peak season and four flights in low season. Coming from Vinh or Hanoi in Vietnam, visas are available on arrival at the Nam Ka border, which is open daily 6AM-6PM. The bus from Vinh leaves four days a week and takes 12 hours, from Hanoi there is one bus per week.
If you are travelling from Vientiane you can either take VIP buses or local buses. The buses leave from the northern bus terminal and take 10-12 hours. The roads are paved but there are plenty of bends. The bus trip from Vang Vieng takes 7-8 hours. Buses run daily from Luang Prabang via Route 13 and Route 7 and take 8 hours. Shared minivan options to the most popular destinations, Luang Prabang, Vang Vieng and Vientiane, are now offered by travel agencies.
There were two buses running daily from Vinh in Vietnam, going from the main bus station at 6AM (no reservations necessary) (2011). Vinh can be reached easily by train from Hanoi or Ho Chi Minh City.