does this circuit use conventional current?

In the reader response section in Nuts & Volts last month, a reader asked if it was possible to detect when someone was on the phone or not (he had some setup where a computer shared the same line and didn't want to interrupt the person on the phone).

I'd like to put this circuit together, but not sure why ground is attached to the output of the NAND gate (rightmost GATE). Is this circuit using conventional current? Part of me says no because of the way the LED is connected (current flows from bottom to top), but does it flow into the output of the NAND gate? :/

I appreciate any help on this. Unfortunately tracing schematics is an area where I get confused. Are there any good books or Internet sites that focus on tracing schematics to figure out how they're working?

Here's the picture of the circuit: http://img208.imageshack.us/img208/7791/busy2wf.jpg

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Mike
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