Hong Kong
South Korea
Japan
Taiwan
 
Correct Answer: Japan

A brief explanation why…

More than 90% of the mobile phones sold in Japan are waterproof following a large number of instances where handsets were damaged by water, not least because of the tendency of Japanese women to bring their phones into the bath. Casio's Canu 502S (aka G'zOne) was released in 2005 as the first waterproof feature phone and in fact there is an entire market of waterproof electronics including TVs.

Although few companies offer such lines for international markets, many device makers located outside Japan will create waterproof handsets and the like to be imported specifically for that market. However, it often prevents devices from being offered in Japan, such as LG's modular G5, which isn't fully sealed because of its removable components.