For all we know those reviews may have predated v3.11NA firmware. You are not the only one having issues with VOIP/ATA adapters. There is another discussion going on at...
http://forums.dlink.com/index.php?topic=5716.0
I'm not recommending it but it seems that the only solution for the time being is to revert back to 3.01 firmware. Hopefully D-Link gets serious about this and issues another firmware update for the DIR-615.