In this month's Scientific American I took a big-picture look at all the different ways people have invented to input text on phones that don't have keyboards. You can have speed without much accuracy (dictation), you can have accuracy but not much speed (on-screen keyboards)—and sometimes you can have software assistance to get your typing done faster and more accurately (predictive-text keyboards).
Both Android phones and iPhones let you install alternate on-screen keyboards to replace the one that came with your set. Herewith: some capsule summaries of the different approaches.
Swype and SwiftKey: These may be the most famous alternate keyboards. They offer very good predictive text (including three words above the keyboard that the software thinks are the most likely you're about to type). They attempt to learn from your typing to make their predictions more accurate. And they also let you swipe to type.
That is, you drag your finger quickly and sloppily across the keys on the glass, hitting the letters you want as you go; the software figures out which word you must have been going for. (The built-in Android keyboard now has this feature, too.)
ai.type: This keyboard also offers predictive text and swiping but it also provides spelling and grammar corrections. And a lotof customizability. You can drag to make the keyboard bigger or smaller, change the color and design, and more.
Fleksy: Here we have the keyboard that set the Guinness world record for fastest phone typing. It takes practice to master but it offers some clever twists: You drag your finger to the right across the keys to insert a period or to the left to delete a word.
Minuum: Not all keyboards need to be huge. When you need more screen space, you can swipe down on the Minuum keyboard to collapse it into a single, odd-looking row. You can still type this way, and you can always swipe it back up to full size.
Speed and accuracy are the most important features of a third-party keyboard but they're not the only ones. You may also gain greater customizability; easy typing of emoji (emoticons—smiley faces); choices of "skins" (color schemes and graphic designs); multiple languages; and their own quirky personalities.