Update: A Microsoft spokesperson told AppleInsider on Friday that a version of Skype aimed at Leopard users "will soon be available for download."
Starting last week, Skype users began to complain on the company's forum that they were being locked out from accessing the popular voice over IP service, reports TUAW. As complaints mounted, it was guessed that Skype was no longer operational on Macs running older versions of OS X.
Microsoft today confirmed the change in service (albeit in a roundabout way) in an answer to a question regarding Skype compatibility with OS X 10.6 Snow Leopard, which will for now remain unaffected.
Skype message board staff member Rene writes:
there seems to be a lot of confusion around this. First, let me assure you that no-one is locking you out from using Skype on OS X 10.6 - 10.8 and there is no need to upgrade to Mavericks or (the new OS X now in dev preview) Yosemite if you don't want to.
All OS X 10.6 - 10.8 users can head over to http://www.skype.com/en/download-skype/skype-for-mac/downloading/ and get version 6.15. This is a very solid release and you can still use all of the main features without any problems (i.e. group video, group chats, screen sharing etc).
Note that you should only use the link above, it serves you with a correct update for your OS version, direct links (to DMG files) can work, but are not guaranteed to do so.
That said, we still encourage you to stay up to date, meaning upgrading to Mavericks and getting the latest Skype.
Hope this clarifies things a bit.
If you have problems updating, please let us know in this thread and I'll try to help you.
For reference, Apple's OS X 10.6 Snow Leopard requires only that a Mac have an Intel processor to run, meaning machines that are absolutely unable to run Skype under the new policy are some eight years old.
For those with older Macs, industrious users have fashioned workarounds, including a method of blocking the software's update mechanism from connecting with update servers, though these bootstrapped solutions are hit-or-miss.
In June, Microsoft said it would "retire" older versions of Skype for both Mac and Windows over the next few months, forcing current users to upgrade to the latest builds for uninterrupted service. At the time, the company noted users with Skype for Mac (6.13 and below) and Skype for Windows (6.14 and below) would be unable to log in until they update.
The latest version of Skype for Mac is 6.19 and which can be downloaded for free from the company's website.