you can change the travel date up to a year. within the year, you can change the date to a different date without fee?

If I booked a ticket Oct 9th 2012 for travel date of December 30th 2012 but I couldn't travel on travel date and I call to extend the travel date to July 2013, Can I call again to have the travel date changed without charge? I can change as many times as I want without fee for up to a year from flight booking date??