Your android phone will do the hard work of sending SMS. It will do this automatically using the Android application that comes with SMS Gateway. When you send an SMS using the API, it will first be stored in your server, then it will be directed to the application installed on your mobile.
Sendapp SMS Gateway
Create your SMS gateway using your Android phone
All the messages you receive on your Android device will be visible in your SMS Gateway admin panel. You can even link your script to reply to the incoming message or run some other command in response to a certain message.
Host your SMS gateway on your server. You can use it in your applications using the API (C #, PHP etc.) provided with SMS Gateway. All messages sent using the API will be stored on your server. It will also track the status of all messages.
You can also use excel files to send messages. You can use xlsx, xls, ods or csv files. There should be numbers and messages in the first two columns of the Excel file to do this. If you have any other data in the remaining columns, it will be ignored.