I am riding on the success of converting an ATA into a paperweight in less than 2 days after I bought it that it's surprising something works. It's surprising that this "hack" to get the phone working with iSync wasn't that complicated. James Lloyd has a page where he has listed the changes needed for most Series 40 phones. The hack there extends a base plugin for S40 3rd edition, and does not work for later revisions. (^F in the comments give a lot of frustrated users). For my reference, I had the information that the 8800 is a supported phone on iSync, and that uses the same version of S40 as my phone.  A little more googling revealed this howto for writing iSync plugins. Firing up the isync plugin maker, I got the GMI and GMM in less than a minute. a s/8800/2600-c2/g job on the relevant lines gave me a working support! Contact and Calendar syncing works now, and I haven't run into any problems. Now lies the much more daunting job of keeping my Yahoo contacts, Gmail contacts, Plexo and OSX address book in sync. Just so that I have a backup of my changes in the interwebs, here's a copy of the modification I made to /Applications/iSync.app/Contents/PlugIns/ApplePhoneConduit.syncdevice/Contents/PlugIns/PhoneModelsSync.phoneplugin/Contents/Resources/MetaClasses.plist

    <key>com.nokia.2600c</key>
    <dict>
        <key>Identification</key>
        <dict>
            <key>com.apple.cgmi+cgmm</key>
            <array>
                <string>Nokia+Nokia 2600</string>
                <string>Nokia+Nokia 2600 Classic</string>
                <string>Nokia+Nokia 2600c-2</string>
            </array>
            <key>com.apple.gmi+gmm</key>
            <array>
                <string>Nokia+Nokia 2600</string>
                <string>Nokia+Nokia 2600 Classic</string>
                <string>Nokia+Nokia 2600c-2</string>
            </array>
        </dict>
        <key>InheritsFrom</key>
        <array>
            <string>family.com.nokia.series40.bus.bt</string>
        </array>
        <key>Services</key>
        <array>
            <dict>
                <key>ServiceName</key>
                <string>com.apple.model</string>
                <key>ServiceProperties</key>
                <dict>
                    <key>ModelIcon</key>
                    <string>NOK8800.tiff</string>
                    <key>ModelName</key>
                    <string>2600c</string>
                </dict>
            </dict>
            <dict>
                <key>ServiceName</key>
                <string>com.apple.synchro</string>
                <key>ServiceProperties</key>
                <dict>
                    <key>MaxEventDescriptionLength</key>
                    <integer>500</integer>
                    <key>MaxEventLocationLength</key>
                    <integer>153</integer>
                    <key>MaxEventSummaryLength</key>
                    <integer>500</integer>
                    <key>MaxPhoneNumberLength</key>
                    <integer>36</integer>
                    <key>SyncMLItemMetaOverrid</key>
                    <true/>
                    <key>SyncMLLargeObjectSupport</key>
                    <true/>
                    <key>SyncMLMaxObjSize</key>
                    <integer>10000</integer>
                    <key>SyncMLNumberOfChangesSupport</key>
                    <true/>
                    <key>SyncMLTemporizeAfterConnect</key>
                    <false/>
                </dict>
            </dict>
        </array>
    </dict>

If you have a 2600c and you're looking to get it working with iSync, I'll be interested in hearing your success. Heck, if there's demand, I can create a dmg wrapping up these changes.