If you have recently jailbroken your iPhone/iPod/iPad with the newest and easiest jailbreak ever – JailBreakMe.com, then you may have also encountered the problem with Skype not multi-tasking or not running in the background. There is a simple fix that involves updating your Mobile Substrate through Cydia. Simply do the following and Skype should start working for you again:

1. Open Cydia
2. Tap Manage
3. Tap Upgrade – You’ll need to update all packages, Cydia, Mobile Substrate, etc.
4. Once complete, it should prompt you to reboot your device. After reboot, Skype should work properly.

If you’d like to see more info about Mobile Substrate, you can look here: Cydia Mobile Substrate Package