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Nice I will work on getting this implemented this evening.

Can the same thing be accomplished using the API with a CURL command and putting the Super Admins login details in the header?

Login your app with an Admin user (user extension with the Super Admin role. E.g. the default 101 extension). Read account extension and parse the response to make a list of extension ids (Note: extension id, NOT extension number!). Then read the message store of each extension by specifying the extension id for that extension in the query path. If you have an account with a large number of extensions (> 50 extensions) , do take care of the API rate limit. Here is a snippet code in Node JS, showing how to extensions and read the message store of other extension.

var extensionList = []
function get_extensions() {
  platform.get('/restapi/v1.0/account/~/extension')
      .then(function(resp){
          var jsonObj = resp.json
          for (var record of jsonObj.records){
              extensionList.push(record.id)
          }
          readExtensionMessageStore()
      })
      .catch(function(resp){
          console.log("Something went wrong.")
      })
}

function readExtensionMessageStore(){
  async.each(extensionList,
    function(extensionId, callback){
        var endpoint = '/account/~/extension/'+ extensionId +'/message-store
        platform.get(endpoint, {
                   dateFrom: '2018-01-01T00:00:00.000Z',
                   dateTo: '2018-07-31T23:59:59.999Z',
                   phoneNumber: "1223343434"
                   messageType: 'SMS'
          })
          .then(function (resp) {
            var jsonObj = resp.json()
            console.log(extensionId)
            console.log("=========== EXTENSION MESSAGE STORE ===========")
            console.log(JSON.stringify(jsonObj))
            console.log("+++++++++++++++++++++++++++++++++++++")
          })
          .catch(function(ex){
            console.log(ex.message)
          })
    }
  )
}