Could a wizard use the magic mouth ritual on an item, telling it to repeat the Verbal Component of a specific spell when the wizard touches said item, thus allowing a wizard to cast a Verbal spell without speaking? I realise that this would only ever be situationally useful, but I'm just curious to see if I am interpreting the rules on both the Magic Mouth ritual and verbal components correctly.
PHB, pg 203
If you can't provide one or more of a spell's components, you are unable to cast the spell.
When you cast Magic Mouth you are embedding a message in a usually mundane object to be spoken at another time. It is physically the object that speaks the words. Since you are not providing the spell's components, you are unable to cast the spell.
No, it would not complete the spell properly.
Casting a spell involves focusing the mystical energy to do what you want. As you allow the energy to flow through you, your esoteric intonations, your practiced gestures, and your carefully prepared bits of fluff and pinches of dusts all serve to focus the spell to its purpose, guiding its energies.
When you are casting the spell and you speak the words, you are focusing the energy that is flowing through you. It could be any source speaking the words that is not you, and it would still not focus the spell correctly.
It's the same as spells that have a Verbal component only. You can't simply mumble the appropriate words and have the spell go off as often as you'd like. It also requires that you channel the power to make the spell work.
If I were DM'ing it, I would allow an exception for a warlock who has taken the "Voice of the Chain Master" invocation, and has their familiar in physical contact with them during the casting, due to the already strong metaphysical bond between a familiar and its master.