@nix666 it uses mariadb and odbc, I don't consider those to be particulalrly SoC friendly. About half of the space used is dedicated to this two components.
If you really need gammu you can install the firmware build system and look at the gammu code to see if you can slim it down. An easier option might be to upgrade to a 2+, Pro or a Dock with a USB key.
Sorry I cannot be of more help.