No. Only your registered supporters who are using the Lumin App can send your messages, but anybody can call you since your Lumin screen has a corresponding landline number assigned to it. The number of your Lumin Screen is located at the top of the Dial Pad inside "Phone".
Please speak to your Primary Supporter if you would like to add more Supporters. They can easily add more Supporters to your Lumin Screen through their Lumin Supporter's App on their phones.