WhatsApp co-foundertook time off from his hectic schedule at the Mobile World Congress in Barcelona, on what was his 38th birthday, to talk to ET about the $19 billion deal with Facebook and what advice he would give entrepreneurs. Edited excerpts:A: I was interviewed for Facebook but nothing really worked out.A: I got an iPhone and I started to experiment trying to build an application for an iPhone. First, we focused on using your address book. Everybody else was using user names or pin codes, like BBM… Skype you had to get an approval… these were all complicated processes. We just wanted to simplify it. If you have somebody’s phone number in your address book, you are on.We were the first guys to do it, we were actually the first mover. Everybody else came in and tried to copy us, but they weren’t successful. We were global from day one. We focused on translations, we added Italian, German, Spanish, Russian, into the applications from day one because we understood that it’s the power of communication, that people want to communicate with people in other countries.We hired really smart people, our first set of engineers was extremely talented and allowed us to build a foundation that enabled us to build everything on top of it.A: Today, it’s a simple one – we are free for the first year of subscription and then it’s a dollar a year. There are no plans to do anything else. We are pretty happy with this. For voice, we haven’t finalized it internally yet but we might do something different in terms of implementation but fundamentally it will be very similar.A: We are going to make sure voice works just as well. I understand that there are bandwidth constraints, network constraints, but we will take the same approach to voice that we took to (messaging) five years ago, which is focus on quality, simplicity, performance so that it’s the world standard for voice just as messaging it’s the world standard.A: The important thing to talk about here is not the price. Mark asked me to be on the board of Facebook and I’m extremely flattered. We talked about this as a partnership and not as an acquisition. WhatsApp will continue to remain independent. There are no changes planned to the product. Nothing really changes from the user point of view. And, so when we were talking about this deal, we were not as interested in terms of the numbers but as a partnership between two great companies who share the same vision.A: Should be none. We are still an independent company and we will continue to be an independent company even after the deal closes. But we do plan to grow, absolutely. We are going to have to hire more people to support more users and build new things like voice.A: I only have one idea, that is WhatsApp, and I am going to continue to focus on that. I have no plans to build any other ideas. The day the deal closes, it’s going to be like any other day when we will go back to work.A: It’s rewarding but again I don’t spend any time thinking about it. A lot of my time, effort and focus is spent on WhatsApp. And that to me is more valuable and rewarding than to work on anything else.A: None. Still the same. We still have a lot of work to do. We still have a lot of people who will get onto smartphones, we still have a lot of bugs to fix and improvements to make. Our mission is still not done.A: We have always had people copy us. It’s not shocking, if anything it’s flattering. But what’s important for us is to continue to get our product right. I spend more time worrying about ourselves, that we’re doing the right thing.A: Probably not to this level. The size of this deal shows how important communication is in today’s world. Communication is at the very core of our society. That’s what makes us human.A: It’s a very critical market for us. Ironically, I grew up watching Indian movies as a kid in Russia. I am quite familiar with Bollywood. I grew up watching Disco Dancer, I watched it some 20 times as a kid. India is important from a personal level too.We want all smartphone users (in India) to be on WhatsApp. Then if that number is a billion, then it’s a billion. Currently, over 40 million. So we still have some ways to go before we hit a billion.A: Hopefully soon. Are you inviting me? I wanted to for a long time. My schedule is a little busy but hopefully this year.A: Focus is an important part of it. A lot of times people start out with a lot of good ideas, but then they don’t execute. They lose the purity of their vision. You end up running around in circles.Hiring smart people, smart engineers. Focus on users right from day one.A: We haven’t decided yet. We will think about it when we come back.A: I have work to do. I get on a plane and I go back and have to go back to the office and work.