Songkhla province, or more specifically Hat Yai, is probably the easiest place to get to in the deep south. No matter where your ultimate destination may be, if you're heading towards the deep south, your trip will probably involve a stop in Hat Yai.
Planes
Hat Yai is home to an international airport with connections to Kuala Lumpur and Singapore as well as Bangkok and Chiang Mai in Thailand. There are around a dozen flights a day between Bangkok and Hat Yai. Flights are operated by the national carrier Thai Airways, budget carriers Nok Air and Air Asia.
The airport is about 12 kilometers (8 miles) from town. Most hotels will pick you up for a fee of around 300 Baht. There's also a car service at the airport for about the same price into Hat Yai, or 500 Baht to Songkhla town.
You can find more information about Hat Yai International Airport at our dedicated on-line guide to Southeast Asia airports, Asia-Airports.com.
Trains
The Hat Yai (or 'Haadyai') Rail Station
The train is a large reason for Hat Yai's being. The city is where the two lines running up either coast of Malaysia come together. So, you can reach Hat Yai by Train from Singapore via either Kuala Lumpur and Butterworth or through Kota Baru; or you can come from Bangkok in the north down to Hat Yai.
Buses
Like the rest of Thailand, inter-city buses are available between Hat Yai and most anywhere else. Your choices are both air conditioned and non-air conditioned buses. You can also travel from Singapore, Kuala Lumpur and Penang to Hat Yai by bus.