The GBATemp forum reports that SvSIP, a free native homebrew application for Nintendo DS gaming handheld that allows users to make free Voip SIP calls through WiFi using a free SIP provider (list of Voip providers), is available for download. The application requires the storage card to be dldi patched in order to be installed. DLDI is an addon that increases homebrew compatibility for different devices by letting you patch homebrew to work specifically with your device.

Instructions for usage:

Nintendo DS Voip SIP

+ Uncompress and extract files in the Zip archive to the filesystem root of your memory card.
+ Create a directory called svsip.
+ In this directory, define parameters of your SIP account in config.txt.
+ Use another application like Mario Kart DS to configure WiFI WLAN.
+ Press ‘A’ to quit application.
+ A log file is created in the svsip directory.

The config.txt included with the application has inline comments and examples to help you configure your Vop-SIP provider. An example of Voipbuster’s configuration can be found here.

Download SvSIP for Nintendo DS here