To add fldigi to the task launcher, I created the file fldigi.desktop in /usr/share/applications/hildon.

[Desktop Entry]
Encoding=UTF-8
Version=1.0
Type=Application
Name=fldigi
Exec=/opt/fldigi/bin/fldigi --font sans:16
Icon=fldigi
StartupWMClass=
X-Window-Icon=fldigi
X-HildonDesk-ShowInToolbar=true
X-Osso-Type=application/x-executable
Terminal=false

Then copy /opt/fldigi/share/pixmaps/fldigi.xpm to /opt/share/pixmaps/ or set up a link.

fldigi should show up in the list of apps.
(post edited to add proper icon and increased font size)