# Mathematical Background and Algorithms of a Collection of Android Apps for a Google Play Store Page
## 1 Introduction
### Vocal SMS Writing and Reading App for Visually Impaired People  
We will present the mathematical background and algorithm for a voice SMS app. SMS (Short Message Service) messaging is one of the most used means of communication, due to its simplicity and speed [1]. SMS messaging is quite an old form of communication, being introduced in the 1980s. It has survived quite a few generations of mobile networks, and it is quite often used even in 5G networks [2]. It has the advantage that the receiver is not interrupted in their work, giving them the possibility to read the message and respond when they have some free time [3]. SMS messaging outlived MMS (Multimedia Message Service) messaging and coexists with modern chat clients that communicate over the Internet [4]. SMS is still popular due to its accessibility and the possibility of reaching places without Internet access, with much greater coverage than chat clients. It also has a guarantee that the message it is sending is the same, since it is a paid service [5]. The fees for SMS messaging are not high; some operators have prepaid options to send a specific number of SMS messages at a fixed price, which greatly reduces the price of a message, and SMS transmission is almost free [6]. SMS messaging is a very inexpensive and easy way to communicate, but there may be a way to make it even simpler [7]. There are problems such as the fact that there are people who cannot use the system or situations in which it cannot be used [8]. This can be the case for visually impaired people, children who have not yet learned to write, busy people who have no free hands, or car drivers. It would be a good idea to create a system in which SMS messages can be handled vocally, like a phone call, but for the price of an SMS message. This can be achieved using speech recognition and text-to-speech software. The interaction is made vocally through speaking and hearing, the system performs the speech-to-text and text-to-speech transformations, and the message is sent for the reduced price of an SMS message.  
[PERSON] et al. (2020) introduced an application designed to manage schedules, send emails, and read SMS messages, all through voice commands. This system allows users to execute tasks by vocalizing commands that are processed by a Speech Recognition Engine (SRE) and translated into text or corresponding actions [9].  
In Table 1, a comparison of the presented vocal SMS app with the state of the art can be seen.  
[PERSON] et al. (2021) concentrated on creating a mobile application aimed at automating SMS systems via voice conversion methods, particularly tailored for people with visual impairments. This app allows users to compose and access messages using voice commands, thus improving their independence [10].  
Creating a vocal SMS app requires the possibility to access the user's SMS database, which is harder in each newer Android version due to restrictions for the privacy of the user. Harder-to-obtain databases mean more coding and sometimes forms to be filled in and accepted by Google. Another requirement is to have a good text-to-speech and speech-to-text software to generate text for SMS vocally and read a received SMS out loud. The goal is to make an SMS client that can be used for vocal phone conversations by visually impaired people, drivers, or busy people. Until now, no app has succeeded in this for some reason, and none of them in the presented way.