Hello there. I would appreciate your assistance.
I am building an app, which aims to activate a gate and several other LEDs. The means of communication is in telephone communications in GSM communication.
I have a SIM900 card and an Arduino card.
I would be happy if you would send me information guides to promote the project.
Thanks
Hello @ido_bason,
I can tell you two solutions: one is to take a look to my post in the IOT section, called :
A BT Gateway between a smartphone and Arduino to control SMS-OT (like I-OT)
In this post I show how to use an old smartphone to behave like a gateway toward an Arduino.
The aim is to send SMS's to the old phone wich is connected by means of the BT to an Arduino board that actuates commands. In this case the old phone is in place of a SIM900: it allows you to control your home devices by sending one (or more) SMS to it.
The second is: I have written a code for the SIM900 and an Arduino board to remotely control the heating system of my country house (when we were still allowed to reach our second houses before the multiple lock-downs, here in Italy 
) Of course I have written the user interface to send SMS's to the SIM900 in AI2.
Then, solution 1 is costless: you just take off from a remote corner of your desk drawer a forgotten phone and you give it a second life. Just retrieve the linked post and you have all: code and documentation written by me in English (my poor english :-))
The second costs you a SIM900 and a lot of tricky code on Arduino side.
If you prefer this second solution I can send you the AI2 code together with the Arduino code but in this case you shall be aware that all the comments inside the Arduino code are in italian language.
BTW in both cases the result is a remote controller for a (second) house heating system.
Let me know.
Cheers, Ugo.
Hi! I made an application with AI2 for android system that controls a vending machine by voice, keyboard and sms having as interface an arduino uno, sim900 module, relay module, bluetooth module and wifi module. It works well, I tried to increase the connection with whasapp for sending messages when failures occur and it didn't work well. I'm now working on it.
Hi, I have posted here some Tutorials about AppInventor and Arduino, maybe can help you.
Thank you very much, I really appreciate your help and thank you for your time. I'll try both ways and update you. 
WOW COOL , Thank a friend.
Dear @ido_bason,
feel free to contact me, should you experience any trouble in programming the SIM900.
Please be aware that some pins are very "tricky" and the documentation that you can retrieve from the web is not always clear enough. To this purpose, take a sight on the comments into my arduino code, to avoid "unespected behaviors".
Cheers, Ugo.
Tks.
Please, see my channel https://www.youtube.com/c/NSLABTUTORIAIS
There aremany kinds of communicatons to Arduino UNO: C#, TCP, Python, Elipse, Tkinter, Proteus, etc and off course APPInventor