background_sms 0.0.4

The main purpose is to send sms from background and headless.You can send sms whatever the phone state is in app or background or headless.

example/lib/main.dart

import 'package:background_sms/background_sms.dart';
import 'package:flutter/material.dart';
import 'package:permission_handler/permission_handler.dart';

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  _getPermission() async => await [
        Permission.sms,
      ].request();

  Future<bool> _isPermissionGranted() async =>
      await Permission.sms.status.isGranted;

  _sendMessage(String phoneNumber, String message, {int? simSlot}) async {
    var result = await BackgroundSms.sendMessage(
        phoneNumber: phoneNumber, message: message, simSlot: simSlot);
    if (result == SmsStatus.sent) {
      print("Sent");
    } else {
      print("Failed");
    }
  }

  Future<bool?> get _supportCustomSim async =>
      await BackgroundSms.isSupportCustomSim;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Send Sms'),
        ),
        floatingActionButton: FloatingActionButton(
          child: Icon(Icons.send),
          onPressed: () async {
            if (await _isPermissionGranted()) {
              if ((await _supportCustomSim)!)
                _sendMessage("09xxxxxxxxx", "Hello", simSlot: 1);
              else
                _sendMessage("09xxxxxxxxx", "Hello");
            } else
              _getPermission();
          },
        ),
      ),
    );
  }
}