Good examples would be writing "nite" for "night", "4" for "for", "wimmin" for "women". I guess it also applies to substituting final s with "z", as in "wordz". In the way that Prince was prone to. Recently I've seen it a lot in alternative literature and music.
Example sentence: "Nice ... in that album title 'Only Built 4 Cuban Linx'"
I can't find them under figure of speech schemes on Wikipedia. Which is odd, because this sort of rhetorical device seems to me currently more popular than, for example, hysteron proteron.
These stylistic devices are different from “kinda”, “sorta”, “coulda”, “shoulda”, “lotta”, “oughta”, “betcha”, “tseasy” etc., in that these are informal contractions, coming from "natural" speech acts like slurring. This question is about deliberate misspelling for artistic or satiric effect.