That is very specifically a question for your group to figure out.

I don't know what your view is of an RD engineer. But in real life, there are no pre-chewed answers available.

When developing a product, you must write down all your design criteria. Exactly what you must fulfill. And things it would be nice optional extras to fulfill.

Then you must spend a significant amount of time looking around and pondering - what alternative solutions exists that can fulfill all requirements in an economical way, and also have the potential to allow some of the bonus features to be incorporated with or without an additional cost.

After that you have decided what alternative solution that seems best for your specific requirements, you will then have to continue by drilling deeper into the problem. Figuring out all critical problems you can see, so that you can quite soon make a more extensive pre-study of the problems. Creating a test setup with the intended hardware and prove to yourself that you can get yourself past these critical points.

If you fail with finding a solution to the identified critical issues, you may have to go back and reevaluate if you should spend more time solving the problems, or if your selected design solution will not work and if you will have to backpedal and select a different path to your goal. If you manage everything critical (solving restart of modem, sending an SMS. Receiving an SMS. Making sure that no SMS mailbox fills up. Proving the current consumption, ...) then you start fleshing out the final solution. Creating commercial-grade software, finalizing the hardware design. Setting up a full platform to allow you to functionally test the different modules in the system and the complete system. Working on the documentation - user documentation, design documentation for the software and hardware. Test specifications. Any production documents if making it a commercial product.

There is a lot to do. In a school project, you can cut some corners compared to a commercial project, but the big issue with your school project is not the working demo, but all the design decisions your group (not members on web forums around the world) makes. You really can't expect this form to make these decisions for you. YOU must figure out what it means to you if you use a mobile phone, or a boxed GSM modem or a GSM module intended for embedded use. If you communicate using RS232, USB, logic-level signals. You must consider the costs. You must find out the availability of documentation. You must decide what risk it represents to go one route or another. That is the big difference between this being your project, and it being our project. In the end, it is not we who should be graded. And it isn't we who are expected to learn from this project...