SMSD is an iPhone SMS management application coded by Amrut Joshi.
Release notes:
SMSD supports 1.1.3 firmware from v0.2.3beta1. But there are some issues. Since 1.1.3, apps are executed with less privileges. Because of this, apps cannot start Services. SMSD also has an option to make it a default SMS app. This is a hack which also requires higher privileges. In short, SMSD notifier and SMSD default app options will not stick if you are on 1.1.3. But there is a workaround.
This is how you enable SMSD Notifier and SMSD Default App preferences in 1.1.3. You need to run SMSD using ssh or Term-vt100. Run following command on the commandline :
# /Applications/SMSD.app/SMSD
This will start SMSD on your iPhone. Go to More->Preferences and change the preference you want. Since this is executed with root permissions, these changes will stick.
You need to restart your phone if you change default app preference.