Microsoft has released a beta version of the Skype client for Windows Phone. The launch of the beta marks the first time the newly Microsoft-owned voice and video calling service is available on Microsoft's smartphone platform.

The application handles Skype's core functions: voice and video calling, plus text chatting. Video chatting is, naturally, greatly improved by the presence of a front-facing camera. However, it works without, as long as the person you're talking to doesn't mind looking out the back of the phone rather than at you.

In brief usage, it all seems to work as expected. Call quality sounded reasonable, over both Wi-Fi and 3G, and video seemed to work (though we lack any handsets with the front-facing camera, so it was not entirely useful).

Microsoft is promising a final release in April and, judging by the state of the beta, there's plenty of work before the program can be considered "stable." Skype's own blog notes a number of flaws with the application, including a number of crash bugs.

Of even more concern is the program's limited featureset. For example, many aspects of contact management are missing from the phone application. These are relatively minor concerns and can easily be fixed. But one major problem has no easy remedy: the program does not function at all in the background. Skype calls can be made and received when it's running in the foreground, but as soon as you switch away—even mid-conversation—the application goes offline. Want to check a detail in an e-mail so you can tell the person you're calling? You'll have to hang up first.

Though Windows Phone 7.5 introduced new multitasking capabilities, allowing applications to do things like play music in the background and run periodic scheduled tasks, it only supports certain scenarios. VoIP is not one of those supported scenarios.

This is in contrast to, for example, Apple's iOS. Though iOS has a similar approach to multitasking—certain scenarios are supported, but it isn't a free-for-all—Apple included support for VoIP applications. These applications can keep a network connection to a VoIP service open persistently, so conversations can be continued even when the application is in the background.

When on a call, iOS also changes the status bar. So even if the application is in the background, it's clear you are still connected. Windows Phone lacks any similar facility.

The original release of Windows Phone 7 in late 2010 had an API that was pleasant and easy to use, but severely limited. Windows Phone 7.5, codenamed "Mango," filled almost all the gaps in the API. But as we noted at the time, the VoIP gap was left unfilled.

The purchase of Skype and the release of this beta application serves to highlight this platform omission. The application's deficiencies will no doubt be fixed by the Skype team in coming weeks and months. The result will be something that is functional and somewhat useful, at least for outbound calls. The platform changes, however, need to be made by the Windows Phone team. Until they make those changes, Skype can never be a great application.