SMS not working in 4.7.23
Searched the www directory for files containing 'editMessageDetails' (grep -inr "editmessagedetails" /var/www/) and compared the result for two different civi installations. Faulty installation had many files with this string in templates_c and the tmp directories. Cleared these &amp; problem vanished.

This can be achieved by:


Clearing the cache via CiviCRM UI - docs in wiki
Executing same via CLI, eg cv api System.flush (or equivalent drush, wp-cli commands)
Manually removing the directories and files beneath templates_c (and tmp?) directories.