have main office pfsense firewall configured like this:

local networks WAN -> internet LAN -> local network VOIP -> IP phones

need to connect remote offices (multi-users) and single remote users (from home) use IPSEC or OpenVPN to build "permanent" automatically connecting tunnels from remote location to main location.

in remote locations, network will look like this: WAN -> internet LAN -> local network multiple users VOIP -> multiple IP phones

in order for the IP phones to work they have to be able to "see" the VOIP network and the VOIP server back at the main office

for single remote users ( like from home ) the setup will be similar but only one phone and one computer

so questions:

best way to tie networks together? IPSEC or OpenVPN can this be setup to automatically connect ?

any issues/suggestions with that design/topology ?

QoS or issues with running the VOIP traffic over a VPN throughput, quality etc.. obviously depends on remote locations connection to some degree