In America, you have only one way to type alphabet using telephone. 2 for ABC, 3 for DEF, etc.
In Korea, there was no national standard until last year so each mobile company came up with their own versions. Some of them were total nonsense in early days, but this is one of the few brilliant ones. No wonder it became the standard.
All the vowels are inputted using the three symbols on 1, 2 and 3. Just like how vowel shapes are designed after. If you don’t know what I mean, check my previous post.
가 = 412
거 = 421
갸 = 4122
겨 = 4221
The vowel disassembly is very easy, and fun.
It is called Ch’eon-Ji-In keypad, which means heaven-earth-human, the three elements of vowel shape modeling.
* image source: http://www.hangeulmuseum.org/sub/future/instrument/han_mobile02.jsp