We are experiencing intermittent dropped calls on 3 phones; (2) 7942s and (1) 7962. The drop calls happen between IP-phone-to-IP-phone and IP-phone-to-voice-gateway. The network consists of 5 Catalyst 4510's, 1 stacked 3750; 1 3845 (voice gateway); and CUCM 6.1(2) subscriber. The network is a hub and spoke configuration. We are routing between VLAN's using IP routing on the one of the MDF 4510.