As a Thai person myself, I'd like to add my personal observation on the uke phenomenon in Thailand. All above threads are quite correct. There is also a TV reality show called 'The Star' where a certain number of teenagers were selected to live and train on singing together. They would have weekly singing competition for a few months and the audience gets to vote for the winner. I think the most recent winner (or maybe a runner-up) was playing the ukulele in her concert and while living in the 'live broadcasted' house. From that point on, girls have been crazy for this little instrument because it looked like it's easy to learn and play, as well as carry.
Many people bought the ukes based purely on their appearance. I went to Ribbee a few times last summer to check what types of ukuleles they carried. To my surprise, many people just came in and bought the Spongebob Square pants ukulele (for 1,800 baht -- roughly around $60) without even trying to hear what it sounded like.
I wanted to try the Mainlands too. But the sales persons told me that they were all sold out. (Now back in the US, I'm waiting for the Mainland to be available again.)
Price wise, I was surprised that most of the ukes were not much more expensive than in the U.S. I thought the prices in Thailand would be much higher because ukuleles seemed to be a trend, but they were not. It was only hard to find one
You may see lots of teenagers carrying their ukes around on the weekends or even during the school days. But some of them don't even know how to play it. They think they look cool (and hi-so) with the ukes
Some young adults might have bought ukuleles because they thought they could learn how to play it in a short time. After three months, though, the ukuleles become their home decoration ornament, which still look cool. One of my Thai friends here in the U.S. is also doing the same. He bought his Lanikai-21C from Amazon. After a few months, it just sat there in his apartment. So I borrowed it because I wanted to try if I could learn how to play it.
Since then, I wanted to return the uke to him, but he just didn't want it anymore. But I've got my own ukes and still love playing them, hence passing around his to our other friends. Now I've formed a little ukulele community among the Thais here -- all girls though
I am also curious whether this phenomenon is going to be the long-trend thingy or just a fad. Only time will tell.