Unfortunately MobileVOIP calls are not yet available through a BIS service. Please try to activate a WiFi or 3G connection.

The BIS (BlackBerry Internet Service) is a service that provides BlackBerry Smartphone users with access to Internet browsing, allows email messaging, instant messaging using the BlackBerry Messenger service, and more. You know you're connected to BIS, when you see the Blackberry Logo next to the signal bar while browsing. To access a WiFi or 3G network, press the menu key and navigate to the Manage Connections icon.

More info about connecting to a 3G network without BIS can be found here