Here’s my take on this.
Directly recording on an iPhone without an announcement isn’t a native feature, largely due to Apple’s system design. Most solutions are workarounds that rely on external services, often integrated through an app.
The most common method involves a three-way conference call. When you want to record, the app dials a dedicated service number that joins your active call. This third line is what actually records the entire conversation. From the phone’s perspective, it’s just a standard conference call, so no system-level announcement is triggered.
Other approaches might involve using external hardware that captures the audio output, or more advanced software solutions on modified devices that can access the audio stream directly. It’s less about a hidden system setting and more about routing the call through a third party.