This iOS app does basically the same thing as the above method. It starts a call, initiates a second call, then merges the two so it can be recorded. However, instead of calls being stored in your voicemail, they’re stored in the app. Automatic Call Recorder Pro costs $4.99.
To set up Visual Voicemail, tap Set Up Now. You’ll be prompted to enter and confirm a voicemail password. Next, you’ll have the option to choose the default voicemail greeting or record your own. If you want to record your own custom greeting, tap Custom. Once you’ve entered created your password and chosen your greeting, you’ll be able to receive voicemails and view them in the Phone app.

4. By default, your voicemail will be setup with your carrier's generic greeting.
When you first set up your Android phone, it may ask you to record your greeting for the caller. You can also keep the default greeting stored on the device. But, in future, if you want to customize the Voicemail greeting or want to create a new one, then you may need to delete the old recordings from Android. It may not be necessary depending on the Android device model & version; it’s good to know the process.