As someone who at points has had high phone call work, I found it much better to use a VOIP line with a wireless desk phone. The ergonomics are better than a cell phone, the 40-hour talk time doesn't run down my phone battery, voicemails don't clog up my cell phone, I can programatically forward the number to my cell number, etc.
Biggest downside I've found is around recording calls. I'm sure there are ways to do that with VOIP, but I've found it easiest to just use my cell when I have the occasional call I need to record.
Yeah, my job doesn't include phone calls at all, so it seems really alien to me now. Even so, the idea of voicemails still seems quaint and antiquated: they're incredibly inefficient for the listener. If I had a job that involved phone calls, I'd still rather just hang up when I don't get an answer, and instead send a detailed email.
Biggest downside I've found is around recording calls. I'm sure there are ways to do that with VOIP, but I've found it easiest to just use my cell when I have the occasional call I need to record.