Serbs did it too at the beginning of the 19th century and since then (in Serbian) every word is written exactly as it is pronounced.
The rule is: "Write as you speak and read as it is written."[0]
The rule is: "Write as you speak and read as it is written."[0]
The Korean tried inventing an optimal alphabet a few centuries ago and it caught on. [0] Traditional Korean writing (in Chinese characters) has been almost abandoned.
The Korean Hangul alphabet doesn't include all possible sounds but I don't think that's really what you want. All those guttural consonants, tonal vowels, and clicks and snaps and buzzes that are possible add complexity, but the real breadth of words is mostly combinatorial rather than based on having a lot of letters.
[0]http://www.learnkoreanlanguage.com/learn-hangul.html