I know you say it as a joke, but the contact list could be a part of the hidden prompt, at least the names, so that it could then trigger an action with the proper name, which iOS would then understand.
Ideally the model would insert an API call into its output to fetch the contacts first, then make the call.
The scary part is asking the LLM to read your messages. Imagine someone texts you an LLM jailbreak. Siri might not be Siri anymore after it finishes reading.
Just wait a bit.
“Hey Siri call X”
-“As an AI language learning model, I cannot know X from your contacts”