Using VoIP with Enterasys Switches

We are exploring the use of VoIP in our network. We currently are using Enterasys Matrix E7 switches and a XP8600 router. This would need to support a large envrironment, approximately 2500 users +. Would like to here from someone who has implemented VoIP over an Enterasys network, or who is in the processes of doing this. Side question: Any problems or limitations experienced with QoS on this equipment.