This is an open question, but it is a logical followup of my previous question asking for an emoticon keyboard app.
It appears it is not possible to define a system-wide keyboard that supports ASCII emoticons. Instead, specific applications can provide a custom keyboard or another way to easily input emoticons.
So what replacements for the SMS app do provide shortcuts to input ASCII emoticons? For use by people unfamiliar by all those weird punctuations.
I am looking for something similar to the Messaging keyboard on Android. (Thanks to VxJasonxV)
The app should not require a jailbreak.
Bonus points for apps that also display ASCII emoticons graphically.
UPDATE: Now iOS does allow system-wide third party keyboards, so this question is no longer really relevant. However I keep it alive because the answer "no third party app can do SMS" is still correct and useful.
Best Answer
Apple does not allow SMS nor Phone replacement apps in the App Store, so this will never be possible without jailbreaking. Since you indicated you would prefer not to jailbreak, you will not be able to do this.
The closest you will be able to get would be to use a third-party SMS service which may either cost or perhaps force you into using a different phone number for SMS specifically with that app. You will need to review third-party apps available to see if they provide a custom keyboard to do what you wish to do.
Long story short: Built-in? Not possible outside of jmlumpkin's suggestion.