Delete old messages: Checkmark to allow the phone to delete older messages in a thread when the Text message limit or Multimedia message limit is reached. No checkmark keeps all messages.
Text message limit: Tap to set the number of text messages to save per thread.
Multimedia message limit: Tap to set the number of multimedia messages to save per thread.
Attachment storage: Sets where to store your attachments. Choose Internal storage or SD card.
Signature: Checkmark to automatically add a signature that you set.
Callback number: Checkmark to automatically enter a callback number. The default is the phone number, but you can change it to another number.