Remove everything from this directory, apart from 2 files:

/Library/Application Support/SyncService/501

(501 being by uid). The two files to keep are:

BTConduitDefaults.plist
SymbianConduitDefaults.plist

The latter was full of shite so I made it look like this:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.
com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<array>
        <dict>
                <key>kNSSyncDeviceID</key>
                <string>00-0a-d9-e8-b7-3a</string>  <strong><---- change this to your mac address</strong>
                <key>kNSSyncDeviceName</key>
                <string>P900</string>
                <key>kNSSyncDeviceShouldSlowSyncCalendars</key>
                <true/>
                <key>kNSSyncDeviceShouldSlowSyncContacts</key>
                <true/>
                <key>kNSSyncDeviceUseCalendars</key>
                <true/>
                <key>kNSSyncDeviceUseContacts</key>
                <true/>
        </dict>
</array>
</plist>

Then try to repair the phone, it should find it and so does iSync.

Thanks to Steve for this fix