Without too much information it is hard to say, but a few things come to mind. First is asymetric routing. The ASA doesn't being left out of the loop so to speak when it comes to stateful traffic. What might be happening is this: Forward path: Data vlan client -> ASA -> Voice vlan client Return path: Voice vlan client -> UC320W -> Data vlan client Since the return path is different, stateful traffic like http will fail to handshake correctly through the ASA blocking the traffic. (You should see errors on the ASA like "Deny (no connection)" if this is the case.) Additionally, you may want to run the built in packet tracer on ASDM to see if the traffic is theoretically allowed between the two interfaces on the ASA. (Packet-tracer is also available through CLI) Hopefully this helps somewhat.
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