From the TodoToday login screen, enabling the Advanced Options will allow for the entry of a custom Teambox server URL. Disabling the advanced options will revert back to connecting to the default Teambox server https://teambox.com.
TodoToday for Teambox has been tested with a fresh Teambox 3 open source edition installation on Ubuntu 11.04 created using the Teambox Installer script from http://teamboxinstaller.gezere.com/
Please report any issues at support.jabanaki.com