I wonder how anthropological linguists would someday treat modern rap and hip-hop. In German, for example, it's not uncommon for the artist to slightly or not-so-slightly mispronounce words to make them fit a rhyme. Would that help or hinder a study?
For example, I think I've seen "besino" written by a native speaker for "vecino" 'neighbor'.
I imagine it would help. If evidence for that mispronunciation happened consistently, it would be taken as a dialect, class, geographical or cultural thing (or subculture). If it happened consistently over a very short space of time (and there was surviving evidence) it could be confused as a blip, or fashion.
Example:
I'm constantly perplexed why 'where' is spelt as 'were' by so many, but I imagine there are a sufficient number of English-speakers' accents (or a sufficient amount of speakers of a single accent to be significant) where the two words sound similar enough to spell them out on a keyboard as the same.
* descriptions of the sounds by the Roman grammarians
* wordplay, onomatopoeia, spelling errors in graffiti, etc.
* the way in which sounds from other languages (particularly Greek) were adapted into Latin
* the way in which sounds of Latin were adapted into other languages
* comparative reconstruction of the Romance languages
* evidence from metrical poetry, which provides particular clues about consonant and vowel length
A very readable book on is W. Sidney Allen's _Vox Latina_.
[edit: meant to reply to immediately following sister of this post.]