I am experiencing the same issue. The n900 detects Google Talk calls coming from Google Talk. But it does not detect Google Voice calls forwarded to Google Talk. The same behavior occurs if I log into my Google Talk account via the Jabber plugin on the n900 -- calls from another Google Talk account are detected but calls forwarded from Google Voice to Google Talk are not. Pidgin on my desktop box does detect the calls. And of course the calls come through just fine within Gmail.