MOTO X IS THERE A GLOBAL DELETE FOR A FULL MAILBOX ON " MAILBOX FULL" ON TELEPHONE MESSAGES? OR DO YOU HAVE TO PRESS 7 AFTER EACH STORAGE??
There is no global delete. However, you may submit a help ticket to delete all but your last 50 messages .
See here for details
a support ticket can delete all but the last 50 messages
Note: If you have more than 50 saved voicemail messages in your mailbox, you may open a Help ticket to have all but your 50 most recent voicemail messages deleted in bulk.