See also Mikrotik QoS

http://wiki.mikrotik.com/wiki/Voip

Use address-list?

/queue tree
add name="IN" parent=global-in priority=1
add name="OUT" parent=global-out priority=1
add name="SIP_IN" packet-mark=SIP_IN parent=IN priority=2
add name="SIP_OUT" packet-mark=SIP_OUT parent=OUT priority=2
add name="ALL_ELSE_IN" packet-mark=ELSE_IN parent=IN priority=8
add name="ALL_ELSE_OUT" packet-mark=ELSE_OUT parent=OUT priority=8

/ip firewall mangle
add action=mark-packet chain=prerouting comment="SIP Only" disabled=yes in-interface=WAN\
    new-packet-mark=SIP_IN passthrough=no src-address=192.168.0.16
add action=mark-packet chain=postrouting disabled=yes dst-address=192.168.0.16\
    new-packet-mark=SIP_OUT out-interface=WAN passthrough=no
add action=mark-packet chain=prerouting comment="All Else" disabled=yes in-interface=WAN\
    new-packet-mark=ELSE_IN passthrough=no src-address=!192.168.0.16
add action=mark-packet chain=postrouting disabled=yes dst-address=!192.168.0.16\
    new-packet-mark=ELSE_OUT out-interface=WAN passthrough=no
add action=mark-packet chain=prerouting comment="SIP Web Server" disabled=yes in-interface=WAN\
    new-packet-mark=ELSE_IN passthrough=yes protocol=tcp src-address=192.168.0.16 src-port=80
add action=mark-packet chain=postrouting disabled=yes dst-address=192.168.0.16\
    dst-port=80 new-packet-mark=ELSE_OUT out-interface=WAN passthrough=yes protocol=tcp