Live Voice Changer for iPhone Calls

I need an iOS-based solution that lets me speak on a normal iPhone phone call while my caller hears a completely different, yet still natural-sounding voice in real time. The change must be applied live as I talk, not through pre-recorded clips, and it only has to work on standard cellular calls (no WhatsApp, Telegram, or other VoIP apps).

Here’s what matters most to me:
• The altered voice should sound authentic—closer to a believable new identity than a cartoon effect.
• Latency has to stay low enough that a normal back-and-forth conversation feels natural.
• I want a repeatable method or prototype I can test on my own device, ideally delivered as either a standalone app, an Audio Unit / CallKit extension, or any other technical approach you know will pass audio into the phone call path. If a jailbreak or private APIs are unavoidable, please state that up front.

Please outline:
1. Your proposed technical approach (Core Audio, AVAudioEngine, custom DSP, etc.).
2. How you will ensure live processing during regular iPhone calls.
3. A rough timeline to a working demo I can install and test.

I’ll be hands-on with testing, so clear build/run instructions or a TestFlight invite are part of the final hand-off. Let me know any device or iOS version limits so we can plan accordingly.