Hello,
Your requirement can be achieved. Given google voice does not have an official api, it will take make it much more complicated.
Here are the steps
1. This will be a web application
2. Interface will have an address bar and start button.
3. When you provide the address and press the start button, the application will start downloading the file and save it
4. The application will be integrated with google voice to ensure sender of the message is displayed as your number
5. You will have to key in the numbers that yo want to send the message to. This will be a one time activity
6. Application will save the numbers and will provide an interface for you to add, edit and delete those numbers