The fact that plugins frequently break each other resulting in a busted site is a good reason to avoid Wordpress
// That said...
This is my take on an empty WP plugin that establishes itself in the menu system, creates 3 configuration fields in the WP setup table, sets up a custom database table for storing a phone list for text messages.
Sets up shortcodes so you can have an enrollment page and a sent page for an admin who cannot navigate the admin panel (conflict??)
Tries to un-install cleanly.
BEWARE: puts itself high on the left admin menu against WP codex recommendation, because I have never had a single client who did not insist upon that. // //