Qos over vpn help?

Hello,
I have two sites setup with ipsec vpn using nsa 240’s at each location. Both sites have 3mbs T1 circuits and are connected over ipsec VPN. I have an ipbx at each location as well, they are “bridged” so they can dial internal extensions over that vpn tunnel. What is the best way to setup qos for voice over that vpn tunnel? So that when someone from site A dials an extenions of somone at site B over the vpn tunnel, that traffice would get priority over any other traffic? Im not utilizing any bwm at this time, but would be happy to set it up if it needs to be in place first before using the qos. Thanks for the help in advance