No, that's not possible. The application must have a stable internet connection for you to be able to retrieve your account contents from our servers, as well as to create new encrypted messages or perform other operations.
Please note that if you are using mobile data on your smartphone, using 3NCRYPT3D Secure Application will generate data traffic. As such, the costs of such data traffic will be borne by you, as it is when you browse the Internet. Check your mobile data communications plan with your mobile operator before using the service.