In short - it doesn't work. That means if you connect the phone to a computer, you CANNOT get the computer to send a text message for you.
It will give "+CMS ERROR: 314", which means "The sim card is busy".
If you try to send a stored message you will get "+CME ERROR:" - yep - thats right it doesn't even meet the spec and give an error number...
That occurs if you try text mode or PDU mode. It occurs over bluetooth or usb cable. It occurs if the messaging app on the phone is open or closed.
Things you can do though:
You can put a message into the outbox in the "waiting..." state, and then manually send it with the phone ui.
You can read/write all messages from the phone to the pc
You can receive messages, including getting event notifications so you don't need to poll.
If you work for LG, PLEASE consider fixing this...