Forget about messing around with apps. There’s a powerful voicemail handling system built into nearly every big carrier today — and that system almost always includes a system for recording a voice message and sending it directly without ringing the target phone. I will walk you through the process of doing this on Straight Talk (since that happens to be my carrier) but most carriers will have similar systems.
When you answer calls made to your Google Voice number, tap 4 on the number pad. Participants will hear a robot voice state that recording has begun—this is Google's way of keeping you legal; Alphabet Inc. wants no part of a lawsuit. To stop recording, tap 4 again or hang up. You can hit the 4 key as often as you like to start and stop recording.

My iPhone rings for 15 seconds – which is actually eight rings – before it goes to voicemail, but even that’s not long enough if I’ve put the phone down in another room or it’s zipped into a pocket in my jacket.
To turn your iPhone off, press and hold the power button until you see the red power icon and slide to power off appear on the display of your iPhone. Using your finger, slide the red power icon from left to right. Wait about 30 seconds before turning your iPhone back on, just to make sure it completely shuts down.