If you attempt to use Network Manager on a machine which has no wired or wireless network interfaces (a rarity nowdays I know, but they do still exist) the "Dial Up Connections" section which lets you connect and disconnect a modem ppp link ceases to show up.  This makes the entire program somewhat useless on older machines which have only dialup modems.  This is the case in both versions 0.6.5 and 0.6.6 (ubuntu)