I have three IP phones connected to my pbx system and I'm using a netgear smart switch. None of the equipment on my network is using QoS or traffic shaping and I'm able to use all three phones simultaneously. QoS is important when there is A LOT of network traffic but don't try and fry your brain with all of this until you notice severe degradation on the calls. Pfsense is GREAT and a really love it but it may be overkill Check out routerboard 750gl.
http://routerboard.com/RB750GL
http://wiki.mikrotik.com/wiki/Category:QoS

I don't work for, by, or with mikrotik...I just love the products and think it shoul be MORE popular than the name brands at your walmart like netgear, liksys, d-link.

good luck.