Manager of the Windows Phone 7 version really blew-it, big-time. Skype (Miscrosoft) needs to announce support for background task and tile notification support in the next release. Hurts Skype and Microsoft, but more so hurts the customer who relies on the both of you to make this transition happen smoothly.
On this topic, I understand your disappointment and am sorry for the inconvenience.
Between Windows Phone 7 and Windows Phone 8, we completely re-architected Skype so that messages and calls can be received when the app is not in the foreground. Unlike on other platforms, Skype does not "run in the background", even on Windows Phone 8 (which is why your battery life is preserved). The nature of the OS changes means our WP8 "hybrid" app doesn't "just run" on WP7. And, unfortunately, it isn't easy and quick to offer this functionality for you.
Since WP8 was announced, we've spent 100% of our development time in getting a working app for that platform; and we have a lot of work left to go.
This is poor. Sorry to say that! I like my W8 Phone but it is in a very, very early state of a beta und as longer as i use it, so more disappointing is it. is it freeware? w8 and skype are from the same company ... is it nessesary to use the community for testing (and crying). Come on.