The autoconfiguration for users will read the voicemail.conf file, perhaps you were able to login with one of those users. But again, you MUST configure buttons and users for thirdlane by yourself. There are some sample scripts on this very same forum to have autoconfiguration for thirdlane, but YOU MUST change your configuration and write those scripts and call them to have any buttons displayed on screen.
In its default configuration fop2 will only work with FreePBX based systems, but you are free to configure things manually or write your own set of scripts. Is the same as asterisk, asterisk does not come preconfigured with the extensions/phones , you must configure it!. Even thirdlane, you ADD EXTENSIONS to it. Well, you must add buttons to fop2.
Best regards,