If you haven't already, refer to this doc for general phoneview troubleshooting:
http://www.cisco.com/en/US/products/sw/voicesw/ps2237/products_tech_note09186a0080883f88.shtml
There was also an issue with the phone firmware, see this bug: CSCsl46387
The problem affected 7970/7971 phones, the solution was to upgrade to 8.3.3.12 loads. Here is the release note for this bug:
Symptom:
1. Unity PhoneView or any other application that uses HTTP POST to control
an IP Phone does not
work. The phone returns an error "4" which means authentication failure.
2. Host not found error, when 7941/7970 etc. user presses the services button.
Conditions:
1. Occurs if there is some delay between the phone and CUCM (or whereever the authentication URL points). In testing this fails with 25 ms one-way delay (50 RTT) however this may fail with as little as 20 ms RTT.
2. Occurs if phone date is the 1st day of the month at 00:00 GMT for a 24hour period, and network delay of 20ms round trip present