how to get skype to work when the phone sleeps

I got a Samsung Galaxy 3 GT-I5800 with Android 2.1. Installed Skype on it, and when connected to wifi it works. When WiFi is not available it switches to G3. While I use the phone, skype works fine. If the phone sleeps/locks, no one can call me from their PC. I think it's because skype disconnects when the phone sleeps and logs-in as soon as I activate the phone touchscreen. What do I need to do, to get Skype to work and receive calls at all times?