The "E" indicates a command form. But for 1st person singular, it is equivalent to giving oneself a command. Consider the identical in the 2nd person singular command. "E hele ‘oe i ka hale." [I command] you [to] go home. "E hele au i ka hale." Literally, I command myself to go home. But the common translation is more like "I will go home." It sounds like future tense. "E kelekiko au," "I command myself to text," implies it will happen sometime into the future, but is really just a command; might not happen. As Kaimana said, true future tense, "E kelekiko ana au," basically says the same thing, "I will text you," and so the "ana" is dropped in this particular case. (But not every case).
As RonRGB says, the future tense applied to 2nd person singular, looks like "E kelekiko ana ‘oe ia‘u." You WILL text me. It is no longer a command; it is definitely the future. I feel that Kaimana is correct for this prompt, the English translation is slightly off. Sorry for the wordy explanation.
This statement flummoxed me, so I looked up "E." Here it is: It marks not only the imperative mood, but also the intentive mood, stating my intent to text you. So it doesnʻt make it the future tense the way we are accustomed to think, itʻs just that the intent involves the future in a way.
Mahalo for mentioning that! "I shall text you" is totally fine as a translation and I will accept it. The "e" in this sentence shows an intent to do something, and so "shall" or "will" can be appropriate. I tend to forget to add "shall" because it sounds rather Shakespearean to me, and not like something I would usually say in casual conversation. That said, it's absolutely acceptable in my opinion. I would also encourage you to send these kinds of suggestions through Duolingo's built-in reporting system (the flag icon), because those are usually what I see first.
I've been looking for the markers, and when I don't see them, I've just been leaving everything in the present tense. But "I text you" was not accepted. I'm feeling like there are implications in the wording of some of the sentences that I'm missing. Just saying that I really appreciate being able to read all the explanations given in the comments on DL. Extremely helpful to have all the perspectives - Mahalo nui kākou!
In this case, (E) can be a marker for the future. However, it has a less definite commitment to the time frame.
Note: Difference between (e verb ana) and (e).
(E) often translates as (will) while (e verb ana) often translates as (going to).
(E) kelekiko au iā ʻoe. = I will text you.
(E) kelekiko (ana) au iā ʻoe. = I am going to text you.