On some phones, a factory reset can delete everything on the phone’s memory and storage area, including SD Cards. To make sure that you don’t lose the messages / calls on the phone, do the following:

Before Factory Reset: 

Confirm that the backup contains your important messages. You can do so using the Menu > View Backups feature in the app itself or by using the online viewer.

Make sure that a copy of the backup is stored outside the phone. There are a few different ways to do that:

• Configure the app to upload the backup to Dropbox, Google Drive or Email and then create a new backup. Confirm that the backup XML file gets uploaded to the cloud account or arrives in the email.
• Copy the backup file to a computer manually and confirm that the size of the file on the computer is the same as what the app shows
• Manually email the backup to yourself. To do so, from the main screen of the app, tap on Menu > View backups, select the Local tab and then tap on the 3-dots menu on top right and then select Send File.

After Factory Reset:

• Install the app again
• If you uploaded the backup to a cloud account,
  • Tap the Restore button
  • Select the cloud account type on the screen and log in to the correct account
  • The app will select the latest backup file on the cloud account, follow the on-screen instructions from there.
• If you copied the files to a computer,
  • Copy/download the backup file created before the reset back to the phone
  • Change the Backup Folder setting to the folder in which the backup file exists
  • Restore
• If you sent the file to email,
  • Open your email client on the phone,
  • Download the backup file from the email client
  • Tap on the downloaded file and the phone should ask you to select an app to open the file with, select SMS Backup and Restore and then follow the on-screen instructions to restore.