I don't really know anything about different voice effects... I have a commission where someone wants it to sound like its a voicemail. How would you go about that? Any help is appreciated.
Depending on what era of voicemail you're going for, there are a lot of aspects to what degraded the audio quality.
What I would do personally is downsample the recording to 10 or 20 kHz. I might also HPF the recording. Then record it to a low-quality tape and record that back into your DAW.
Alternatively, you could literally sing the part into a voicemail inbox and then sample it from there.