Personally, unless there is a specific need for it I always block internet access to/from voice networks including IP phones. Nonetheless, I realize there are reasons to want to do this and leverage a proxy. With that said, I have not personally tested this configuration BUT technically speaking you should be able to enter the proxy URL at the IP phone device level and it will override the system default (which is blank unless configured otherwise). You need to enter the host and port of the proxy server (e.g., proxy.company.com:80). In looking at the Enterprise Parameter description vs. the device level description of this field, there may be a difference in behavior or simply an old description at the phone level because it states that the proxy configuration is used for http requests from the phone to external (non-local) addresses. However, the Enteprise Parameter states that, if populated, the proxy is used for ALL URL requests. Also - based on the device level description of when the proxy is used, I can also see where this may cause an issue with accessing internal services (i.e., states that proxy is used if URL contains a dot or an IP address in any form). Depending on how you set up your URL parameters, you may be referencing IP's (to avoid issues with DNS) and technically they all contain a ".jsp" as well to reference the particular function being called. Give it a shot and see what happens. If you have issues, it would be worth running a packet capture off the back of the phone to see the traffic to/from the proxy. Based on that, it may be easier to determine where the problem (if there is one) lies and how to possibly work around it.
Hailey
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