If you paid attention during the chats and how the text messages are designed, you might have noticed a trend going into the later ones: the use of emojis has drastically decreased to the point where they are no longer used pretty much at all.
Since the story has you "writing" with the girls, the use of emojis seemed natural and was integrated from the very first chat onwards. They were either inserted into messages directly or sometimes replaced those all together. Combined with an appropriate auditive feedback, these emojis were meant to convey the actual chat aspect of the... chats.
Why use them less? Because we simply don't have many good ones.
These are it. What you see here is the sprite atlas for the emojis you can use out of the box in the TextMeshPro package of the unity engine. And as you can see, the variance is a bit... lacking. It's fine at the start but doesn't leave much room for proper articulation. But more importantly: it would result in repeated usage of the same ones over and over.
Why not buy better / more expansive ones? Fun fact that I also didn't know: did you know that emojis are freaking EXPENSIVE to get the license for? Good ones at least. I never thought about that aspect much and figured we'd use a proper emoji set later down the line.
Since that was no longer possible, the chats transitioned to an implied spoken message system. The text was voiced already anyways, which was not intended to be actual voice messages / calls but was implemented because I hate reading in games and voices add a lot of emotion and recognition value to the girls.
So, right now it's a semi grey line between what's spoken and what isn't. Sometimes a different character comes into the chat, implying that it's more of a phone call. But the player's choices are up for debate whether the MC actually says them out loud. It is very much on purpose that the girls don't reference the MC's "voice" or how he "sounds". The closest implication that the MC is talking happens during Aurelia's "Truth or Dare" chat as she explicitly asks the player to "say" things.
And there you have it: tiny little things like these can shake up how a project progresses with future content. And, as with this one, they can come very unexpectedly.