I downloaded an VOIP App for blackberry called 99 by Factor Lusitano. It has a curious name 90e9.
After you install the App, you'll receive an email, telling you how to set up, and at the end of the email is the username and password you need to login.
If your mobile phone is not connected to Wifi, you need to set up APN or Access Point Name, which is a gateway between your GPRS (or 3G, etc) mobile network and other computer network. I use Vodafone mobile, so I need to set up APN specified by Vodafone. You may find APN settings by following this route: Options : Device : Advanced system settings : TCP IP : APN settings. APN for Vodafone is wap.vodafone.co.uk, username and password is wap.
When these are done, you will be registered to the network anD ready for call.
Sent from my BlackBerry® wireless device