All the owners of Symbian^1 powered devices are now able to download and install Skype. It offers all the functionality of the desktop Skype app and can use both 3G and Wi-Fi connection.
You can download Skype for Symbian from the official website or from the Nokia Ovi Store.
Currently Skype runs only on Symbian-running Nokia handsets, but soon the app will become compatible with all kinds of Symbian devices (such as Samsung and Sony Ericsson).
For the full list of supported devices you may follow this link.