async def send_sms(hass, user, password, sender_did, call):
    """Send SMS message using multipart form-data like MMS."""
    _LOGGER = logging.getLogger(__name__)
    recipient = call.data.get("recipient")
    message = call.data.get("message")

    if not recipient or not message:
        _LOGGER.error("Recipient or message missing.")
        return

    # Build form data dictionary
    form_data = {
        'api_username': str(user),
        'api_password': str(password),
        'did': str(sender_did),
        'dst': str(recipient),
        'message': str(message),
        'method': 'sendSMS'
    }

    async with aiohttp.ClientSession() as session:
        with aiohttp.MultipartWriter("form-data") as mp:
            for key, value in form_data.items():
                part = mp.append(value)
                part.set_content_disposition('form-data', name=key)

            _LOGGER.error("voipms_sms: sending SMS: %s", mp)
            async with session.post(REST_ENDPOINT, data=mp) as response:
                response_text = await response.text()
                if response.status == 200:
                    response_json = json.loads(response_text)
                    if response_json['status'] == "success": 
                        _LOGGER.info("voipms_sms: SMS sent successfully: %s", response_text)
                    else:
                        _LOGGER.error("voipms_sms: SMS not sent: %s", response_text)
                else:
                    _LOGGER.error("voipms_sms: Failed to send SMS. Status: %s, Response: %s", response.status, response_text)