WhatsApp BULK messaging app.

We are looking to have an APP made that would simply send message to ALL whatsapp contacts i.e All contacts having whatsapp installed on a user's phone as text (no media support needed). The Application would also show delivery information or the data sent through the app should reflect on whatsapp. We are not looking at the broadcast feature where the delivery is limited to users who have the sender as contact, but to all. We are looking to have a system that can pause and resume the sending in a timely fashion to prevent any bouncing etc. Please reply with 'whsapp' and also let me know how you wish to do this. which api will be used? users who do not mention details will be ignored.