I have hosted trixbox before in a ESX environment 5 years ago without issues.
Currently I am using vmware workstation 8 to test freepbx with Twilio. The hardware specs are top notch:
Dell precision laptop m4800
i7-4900mq 2.8GHZ
32 GB ram physical (4gb VM)
Win 7 professional 64bit Host (64bit Freepbx VM 10.13.66, Release Date: 2015)
Samsung 840 Pro SSD (40GB HDD space allocated to VM)
I've managed to fix the audio issues during a live call. It had to do with jitter and NAT. But I am still getting digitized voicemail that sound like they have been slowed down.
I am going to take at the timing issue right now, otherwise I will just test it on a physical machine.