How to Implement “Send SMS on Mobile” Using .NET

Sending SMS messages from a .NET application is a common requirement for:

• OTP verification
• Login authentication
• Notifications
• Alerts
• Marketing campaigns
• Appointment reminders

In this blog, we’ll build a simple SMS sending feature using .NET and an SMS gateway API.

Prerequisites

Before starting, make sure you have:

• Visual Studio installed
• .NET 6/7/8 SDK
• Internet connection
• SMS provider account (Twilio, Fast2SMS, TextLocal, etc.)

For this tutorial, we’ll use:

• ASP.NET Core Web API
• Twilio SMS API

Step 1: Create a New .NET Project

Open terminal or Visual Studio.

Create a new Web API project:

dotnet new webapi -n SmsSenderApp

Move into the project folder:

cd SmsSenderApp

Step 2: Install Twilio Package

Install the Twilio NuGet package:

dotnet add package Twilio

Step 3: Create a Twilio Account

Go to:

• Twilio
• After signup, collect:
• Account SID
• Auth Token
• Twilio Phone Number

Step 4: Configure App Settings

Open appsettings.json.

Add:

{
  "Twilio": {
    "AccountSid": "YOUR_ACCOUNT_SID",
    "AuthToken": "YOUR_AUTH_TOKEN",
    "PhoneNumber": "+1234567890"
  }
}

Step 5: Create SMS Service

Create a folder named:

Services

Inside it, create:

SmsService.cs

Add the following code:

using Twilio;
using Twilio.Rest.Api.V2010.Account;
using Twilio.Types;

namespace SmsSenderApp.Services
{
    public class SmsService
    {
        private readonly IConfiguration _configuration;

        public SmsService(IConfiguration configuration)
        {
            _configuration = configuration;
        }

        public async Task<string> SendSms(string to, string message)
        {
            var accountSid = _configuration["Twilio:AccountSid"];
            var authToken = _configuration["Twilio:AuthToken"];
            var fromNumber = _configuration["Twilio:PhoneNumber"];

            TwilioClient.Init(accountSid, authToken);

            var result = await MessageResource.CreateAsync(
                body: message,
                from: new PhoneNumber(fromNumber),
                to: new PhoneNumber(to)
            );

            return result.Sid;
        }
    }
}

Step 6: Register the Service

Open Program.cs.

Add this line:

builder.Services.AddScoped<SmsService>();

Example:

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddControllers();
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

builder.Services.AddScoped<SmsService>();

var app = builder.Build();

Step 7: Create SMS Controller

Create a controller:

Controllers/SmsController.cs

Add the following code:

using Microsoft.AspNetCore.Mvc;
using SmsSenderApp.Services;

namespace SmsSenderApp.Controllers
{
    [ApiController]
    [Route("api/[controller]")]
    public class SmsController : ControllerBase
    {
        private readonly SmsService _smsService;

        public SmsController(SmsService smsService)
        {
            _smsService = smsService;
        }

        [HttpPost("send")]
        public async Task<IActionResult> SendSms(string mobile, string message)
        {
            var response = await _smsService.SendSms(mobile, message);

            return Ok(new
            {
                Success = true,
                MessageId = response
            });
        }
    }
}

Step 8: Run the Application

Run the application:

dotnet run

Swagger will open automatically.

Test API:

POST /api/sms/send

Example request:

mobile=+919876543210
message=Hello from .NET SMS Service

Step 9: Successful SMS Response

Example response:

{
  "success": true,
  "messageId": "SMXXXXXXXXXXXXXXXX"
}

Complete Project Structure

SmsSenderApp
│
├── Controllers
│   └── SmsController.cs
│
├── Services
│   └── SmsService.cs
│
├── appsettings.json
├── Program.cs

Security Best Practices

Never:

• Hardcode credentials
• Expose Auth Tokens publicly
• Commit secrets to GitHub

Use:

• Environment variables
• Azure Key Vault
• Secret Manager

Example:

dotnet user-secrets init

Sending OTP SMS

Example OTP generation:

Random random = new Random();
int otp = random.Next(100000, 999999);

Send:

await _smsService.SendSms(
    "+919876543210",
    $"Your OTP is: {otp}"
);

Alternative SMS Providers

You can also integrate:

Advantages of SMS Integration

• Fast communication
• Better customer engagement
• Secure OTP verification
• Real-time alerts
• Works without internet on phones

Conclusion

Implementing SMS functionality in .NET is simple using modern SMS APIs like Twilio. By creating a reusable SMS service, you can integrate:

• OTP systems
• Login verification
• Notification systems
• Marketing alerts
• Appointment reminders

With just a few lines of code, your .NET application can send SMS messages globally in real time.