Ran across this reference on the ARRL web site. I don't have an iPhone or else I would give it a try. Might work well for keeping an 'eye' out for band openings.
http://digitalconfections.com/index.php?option=com_content&view=article&id=46&Itemid=54
http://digitalconfections.com/index.php?option=com_content&view=article&id=46&Itemid=54