VLAN over multiple locations

[Eleander]

Ok here we go!

Going to/wanting to implement VoIP on 6 different sites.
All are pfsense firewalls each connected with IPSEC VPN's!
Site A
-> Site B
-> Site C
-> Site D
-> Site E
-> Site F

Site B
-> Site A
-> Site C
-> Site D
-> Site E
-> Site F
and so on! I can't have 1 single point of entrance which routes everything because internet access speeds don't allow me to! i would bottleneck that one firewall/internet connection!

Now I wan't to create a VLAN (eg VLAN VoIP with tag 100) on each of these sites. I have a seperate physical port free on each FW where I can start creating the VLAN. (as test before I implement on the existing one)
Max should be about 25 ip phones/site! Any suggestions?