Apple iPhone 4G - Manual (Page 252)

Korean
Use the 2-Set Korean keyboard to type Hangul letters. To type double consonants or
compound vowels, touch and hold the letter, then slide to choose the double letter.
Vietnamese
Touch and hold a character to see the available diacritical marks, then slide to choose
the one you want.
You can also type the following key sequences to enter characters with diacritical marks:
 aa—â (a circumflex)
aw
 —ă (a caron)
 ee—ê (e circumflex)
 oo—ô (o circumflex)
ow
 —ơ (o hook)
 w—ư (u hook)
 dd—đ (d dash)
 as—á (a acute)
 af—à (a grave)
 ar—ả (a question mark)
 ax—ã (a rising accent)
 aj—ạ (a drop tone)
252 Appendix A International Keyboards