Recording your personal calls is a massive legal gray area, since it's technically illegal to record a phone call when all parties aren't fully aware. So that's most likely why Apple doesn't include the feature baked into iOS.
How to record a call using Google Voice
Within the Google Voice app is a switch that lets you record incoming calls. In fact, that switch also enables other options like conference calls. Here's how to do it.
- Download Google Voice from the App Store.
- Launch Google Voice. You'll have to set up an account and choose a phone number based on your location.
- Tap the three dots on the left side of the screen.
- Tap Settings.
- Tap Calls.
- Tap the switch next to Incoming call options.