Media playback is unsupported on your device Media caption "The more users that use the service, the better the call-experience becomes"

It's a common scene, you're sitting in a meeting and the speaker has been going on for hours, then your phone starts vibrating in your pocket; do you take the call?

You look at your phone but the number is not in your contact list. So is it important enough to run out of the room with your phone held half-up in signal to the others that this is a call too important to miss?

Truecaller may be able to help with that.

"If you download Truecaller you will never have to worry about saving contacts to your phone book, everything will be in the cloud." says Alan Mamedi, chief executive and co-founder of Truecaller.

He recalls his own phonecall-in-a-meeting dilemma as being his motivation to help create the app, which he believes could be on every smartphone across the globe.

"If you receive a call from a number you don't have we'll show that information, if there is a sales call coming in we will warn you about that.

"Or if you just want to make an outbound call in a much better way; by knowing if your friend is available or your friend is on a phone call then you can use Truecaller."

Crowd-sourced data

Truecaller uses a database of more than two billion phone numbers to tell you who is phoning you.

Image caption If there is a sales call coming in, Truecaller says it can let you know before you take the call

On certain smartphone operating systems it will show that person's name, where they are from, and in many cases even display their picture.

It then uses crowd-sourced information to recognise nuisance calls and prevent them ever taking a second more of your time.

"In the UK or US every sixth call would be a spam caller," says Nami Zarringhalam, co-founder of Truecaller.

"People in general get more spam calls than they receive calls from family members. So this is a big issue we're pinpointing and providing a solution for."

Alan Mamedi, goes on to explain how the data is collected: "If you receive a call from a number and we can't detect it, then you, as a user, can actually add that information.

"But we also partner with different data providers to fill in the empty gaps".

Privacy issue

However according to Nishanth Sastry, senior lecturer in the centre for telecommunications research at King's College, London, it's this aspect of the company that is open to scrutiny.

If a phone user shares the names and numbers in their contacts book with an app, that then relays those details to the world, it's not that phone user's information to share, he says.

"It's not their own information they are sharing, it is their friends' information they are sharing.

"And they are sharing this information with people that they don't know. That's a privacy issue for friends - who have never seen the terms and conditions of Truecaller."

Image caption Critics says Truecaller subscribers will also be sharing their friends' information to the cloud - not just their own data

Alan Mamedi, doesn't believe this to be an issue: "We made it super easy for anyone to un-list their number on our website, we don't require any verification or such.

"This has been the case since day one. It's part of our philosophy that it should be super simple to just un-list your number.

"You just go on our website and then it's gone forever."

Fast growth

Now Alan, Nami and their team occupy a series of plush offices. It's a long way from where they first began back in 2009.

"We were sitting in my one room apartment, which was basically just my kitchen and bedroom in the same room," says Nami.

"We started to build Truecaller with servers that we had bought, building an application for our own mobile phones."

Image caption Truecaller says deleting your number from its system is very easy

They then decided to release it and within the first week say they had 10,000 new users.

"We decided to start a company and so resigned from our full-time jobs," says Alan. "Since then we've grown really, really fast.

"We have 200 million users globally. Just last year we went from 100 million users to 200 million. We've definitely seen an exponential growth globally, especially in the emerging markets."

Truecaller, he says, also has a few, less obvious uses.

"One of the cases we've seen in India is women who before they jump in a cab actually verify the cab driver who is calling them.

"We with some confidence can say, hey this is a cab driver who's calling you. Or even say if you have friends in common with this cab driver - and that adds a safety layer which we never thought about in the past."

Global ambitions

Despite adding 63 new users a minute on average since its creation in 2009, Alan has even bigger ambitions.

Image caption Started in a one-room apartment, the app now has 200 million users

"The number one app that people are using everyday is your phone app and no one has innovated in that space.

"Truecaller is changing that. It's making your phone experience more trusted and safer, but also more delightful.

"Our aim is to make a great product that everyone will adopt and have it on every single smartphone across the globe."