Whatsapp on their official blog has indicated a flexibility in their policy. It is going to let business send messages to the people using the service.
This is cost effective, the companies instead of sending SMS (text messages) would be able to send the same messages on Whatsapp. Messages such as doctors appointment, your flight information or any other marketing/promotional will be able to send using the service.
Whatsapp has clearly stated, it does not plan to roll out the advertisements in the messages.