What should Whatsapp do?

Whatsapp has taken over Mobile SMS and has sort of become the defacto messaging standard. They were probably responsible for the fall of Blackberry, especially in India. With constant updates making the App easier to use and more beautiful, at some level Whatsapp is the biggest App on the web. I for one use it a lot more than any other App. So if Mobile is the future, Whatsapp has the most firm footing on that front. Infact whatsapp like google is now a verb in the urban dictionary
The only problem, how do they make money?
At the moment Whatsapp charges the user a small measly amount per year. The amount also depends on the OS and the country. Windows OS and Android is free for a year and after that is $0.99 per year, iOS has a one time fee of $0.99. In India they have not yet started charging. I have not paid for the service and am using it for more than 3 years.
Now Whatsapp cannot start charging higher than they are right now. Users will simply shift to another cheaper App and developing an IM App is not rocket science. Whatsapp should also be wary of Google. The search giant has killed a lot of companies by coming up with already existing services. The most recent being Drive and Keep. They just might tweak their GTalk and make it an effective competitor for Whatsapp.
Whatsapp backs up all their user data. At 10 billion messages a day, that is a lot of storage. To aid further development they do need funds, however efficient they are as a company.

Whatsapp in my opinion has 2 options

• Sell to Google, Nokia or Samsung - make a cool truck load of money and leave. Those companies I am sure are ready to pay top dollar to integrate the world's most popular instant messaging App onto their OS.
• Develop related services and increase dependencies by linking and integrating all those services, just like how Google does. This would make Whatsapp a mini OS under the main OS. 

Recent rumours were that Google was looking to buy Whatsapp for $1 Billion. Now that would put Whatsapp on par with Instagram. But I personally think Whatsapp has more potential and with a little financial backing, can reach for the skies.