I'm running 3CX as standalone VM image on ClearOS+KVM. I don't have any install notes, but I do have some history still left in my bash session:

yum -y install qemu-kvm libvirt virt-install bridge-utils virt-install

systemctl start libvirtd 

systemctl enable libvirtd

bash -c 'cat > /etc/sysconfig/network-scripts/ifcfg-kvm01 << EOF

DEVICE=kvm01

TYPE=Bridge

BOOTPROTO=none

ONBOOT=yes

IPADDR=192.168.1.10

NETMASK=255.255.255.0

GATEWAY=192.168.1.1

DNS1=192.168.101.1

EOF'

..

.

<aside>KVM network Networking</aside>

vi /etc/libvirt/libvirt.conf

systemctl start libvirtd 

virsh net-list

..

.

<aside>Download 3CX image to /tmp</aside>

..

.

 virt-install    --name=PBX    --controller type=scsi,model=virtio-scsi    --disk path=/var/lib/libvirt/images/3cx.img,size=8,sparse=true,cache=none,bus=scsi    -

-graphics vnc,listen=0.0.0.0,port=5950    --network bridge=kvm01    --vcpus=2 --ram=4096    --cdrom=/tmp/debian-8.6.0-amd64-netinst-3cx.iso    --os-type=linux    --os-v

ariant=debianwheezy

..

.

<aside>Install Kimichi as front end to KVM</aside>

yum --enablerepo=clearos-contribs-testing install app-kimichi

service kimchi start

service wokd start

..

.

<aside>On boot</aside>

systemctl enable libvirtd

virsh autostart PBX

I know, I know...world's worst HowTo. But hopefully, it gives you some pointers and let's you know that it can be done.

Failing a complete PBX/ISO solution that 3CX comes as, I'd probably recommend taking a look at FusionPBX (https://www.fusionpbx.com/download.php), following the instructions for CentOS install.

B.

Bump... Anyone?