Many keyboard apps can predict your next word. Download a matrix with 20k English words, showing the probabilities of each word. Arbitrarily choose the first word. Consider the most likely next 8 words for your current word and choose one of them in a way that encodes your 3 bits. Continue until all your data is encoded by groups of 3 bits.
Well, anyone can Base64 anything, and, what's underneath the Base 64 could be binary or ansi or utf-8 or anything. Or encrypted good if you have half a brain. So; Good luck with that.
EDIT: Noone types the message-letters on a hooked-up machine. You prepare / encrypt the payload before you paste it onto the sending computer / device. Anything withing the Base 64 you paste into the message-field should be impenetrable.
