Despite the fact that Microsoft owns Skype, the app for Windows Phone has long been lacking in functionality.
As a nod to that fact, the version of the Skype app released on Microsoft's own mobile OS platform just reached 1.0 status, finally coming out of beta.
As a historical note, however, Microsoft completed its purchase of Skype in October but didn't release any form of client for WP7 until February.
Besides the fancy "1.0" moniker, however, the app itself doesn't seem to have received a lot of care yet. For instance, the ability to run it in the background while you perhaps check on a movie listing, look for a restaurant review or do any other kind of activity that might be handy during a call, you can't. This is kind of a deal breaker to make it a useful app for smartphone owners, especially those with a decision still left as to which platform will best support their activites.
The Skype apps for iPhone and Android have not been without criticsm, but at least have the minimum functionality in tact.