I'm not sure I've followed you,
1.- The link to call works, it uses the user's phone in user's profile page and listing page. It works without any modification. If, for some reason, you use a plugin or a custom field to save a different telephone for each listing, then, you have to made some modifications, and the developer is not required to do them for free.
2.- In your admin panel, under "Plugins > Decent mobile theme" it appears the "admin controle panel", so again, this feature is included in the plugin. Also, in the plugins' dashboard, if the plugin is installed, it appears a "configure" buttons, that redirect to the control panel/settings configuration of the plugin.
3.- You are right, developers should not ask money for features that should be included in the theme or plugin. But as stated before, in this case, it works out of the box. If you use the phone field of the user's profile, it should work fine.