Using One Leg of a Roundtrip Ticket

So, I wasn't aware of this until I spotted this today on Hornfans.com... thought you might find it useful.

If for whatever reason you're not going to take the outbound part of a round-trip ticket, CALL THE AIRLINE AND LET THEM KNOW YOU'RE COMING BACK!!!

I had originally booked a round-trip ticket to see my fiancee. My company asked me to go to Boston last minute for training, and I had them book a one-way ticket to Boston, and then to my fiancee's city. I figured I'd use the return part of my R-T ticket to get home.

NO GO!!!

I just got back from the airport, where they told me since I didn't take the outbound flight on my R-T trip, they cancelled it and sold my seat. They rebooked a flight and charged me an extra $300 to go home tomorrow. All this could've been avoided if I had called them to tell them, but who the hell knows these rules until it happens?