Bumpei Tateno
Country Manager of Thailand branch, Global Business Division, Adways

Credit card penetration which calculated by the number of cards issued is roughly 20% in Thailand, which is much higher than other countires in Southeast Asia. In actuality, however, I think this rate is around 10% because upper class tends to hold multiple cards.
Considering where Thailand is at economically, it is unlikely that the credit penetration will rise in 5 years. Even if the penetration rose, it will still take long to catch up to the mobile field. Despite the situation, Thailand has not introduced neither GooglePlay card nor iTunes card yet.

The pie chart above shows In-App-Purchase ratio by payment methods.

The actual ratio very much depends on each title, but overall in app purchase at App Store is 1.6 times as Google Play. One remarkable finding here is, almost 40 % of all payments are made by prepaid cards which do not go through either App Store or Google Play. These payments take place outside apps: usually bring users from Facebook fan pages to websites and users have to put their serial numbers from their prepaid cards.
As you probably know already, these prepaid cards could potentially be in a gray area, because placing Redeem in apps or bringing users from web pages, apps get banned from stores. Nonetheless, this is one of the quite commonly used payment methods introduced among Thai developers.