Although Steve Ballmer insisted that Microsoft would continue to support Skype on non-Microsoft platforms when it acquired the VOIP company earlier this month, it looks as though that may not necessarily be the case. And the first casualty seems to be Skype's integration with Asterisk, an open source telephony platform.

Digium, the open source project's maintainer, has informed its users that Skype for Asterisk will no longer be available for sale or activation after July 26. According to the notification, Skype has opted not to renew the agreement that allows Digium to utilize Skype's proprietary software in order to turn the open source Asterisk into a native Skype client.

Existing users of Skype for Asterisk won't be immediately affected. "Representatives of Skype have assured us that they will continue to support and maintain the Skype for Asterisk software for a period of two years thereafter, as specified in the agreement with Digium," the memo reads, adding that users of Skype for Asterisk will be able to continue using Asterisk on the Skype network until at least July 26, 2013.

Although ReadWriteWeb editor Richard MacManus argued that Skype's acquisition by Microsoft could take the VOIP service "to the next level" with integration in Windows mobile devices and with Xbox and Kinect gaming systems, it appears that the new frontier for Skype may be inhospitable for open source.

CRN reports that open source telephony has seen steady growth lately, as companies have soft lower-cost but feature-rich solutions, with open-source PBX systems accounting for almost 20% of all PBX sales in North America.

As ReadWriteWeb's Dan Rowinski recently noted, Microsoft's acquisition plans for Skype may include deep integration of the VOIP service into its Lync communications platform - a platform that is certainly a competitor to the open source Asterisk.