batch sending Whatsapp Message

This app is to access my Whatsapp contacts and to send a message to them through Whatsapp's messaging gateway. I have a long list of clients whom I built up over the years and will like to inform them of promotions and special offers through Whatsapp. Rather than having to broadcast within the limits of 25 and going through a hundred times selecting one by one 25 contacts to broadcast every time, I require an android application (or interfacing application to Whatsapp) to access my contacts who are also on Whatsapp, to allow me to select all contacts at once (a select all option), and finally a text box to type my message, and to broadcast to all contacts in batch mode of 25 untill the Whatsapp contact list is finished. This is not for spamming purpose. It is a legit app to be used on my customer list. i have checked that it does not run foul of whatsapp's spamming policy.