What goes in to designing and making a high-specification smartphone?

So what do you want in your phone? What annoys you about it? What would your dream phone look like, behave like or do? HTC, the Taiwanese smartphone maker that has risen from seemingly nowhere in under five years, would like to know.

Three Taiwanese entrepreneurs founded HTC in 1997, making laptops and, a year later, handheld gadgets. It was an original design manufacturer, that is, it built devices to order for other companies, whose names appear on the final product. It was responsible for the O2 xda, a groundbreaking touchscreen gadget using Windows Mobile as its operating system. But then, in 2007 it revealed its first HTC-branded handset, the Touch. Windows Mobile was a widely disliked phone interface, but HTC overlaid it with its own touchscreen interface which made the experience much more palatable.

This developed into the Sense software which every phone from the company features, even though today's handsets use the popular Android and fledgling Windows Phone platforms. Sense is a software "skin" which the company overlays on top of Android and Windows Mobile, replacing Android's icons with classier versions or adding programs such as its signature weather information app. Windows Phone is a tougher platform to customise, but it manages to add its apps in a prominent place.

Although the company's Windows Mobile phones won plaudits, the business-centric Windows software meant that HTC's growth was quieter and less explosive than others.

One of the first handsets to gain attention was 2008's Touch Diamond. The hardware was created by San Francisco-based design company One & Co, who had designed gadgets including the first Amazon Kindle. The Touch Diamond was a compact touchscreen handset with a shiny back picked out in angular shapes – Daniel Hundt, One & Co's creative director, describes it as "business at the front, party at the back".

In early 2009, HTC decided it liked One & Co's work so much, it bought the company. It now designs all of HTC's products. It's a small company with around 20 designers. Based in San Francisco, the minimalist offices had no mobile phones on display when I visited. "Much of the furniture in this office was designed by us," Claude Zellweger, principal and design director at One & Co, says. "We do so many things to make sure we don't get stale."

The first One & Co phone for HTC was the Touch Diamond. The design process can be surprising, Zellweger says. "When we're designing, it's important at the beginning that there's not much judgment but then, like Darwinism, the best ideas rise to the top."

Scott Croyle, vice president of design at HTC and a One & Co founder, explains how one phone came about. "With the Incredible S smartphone, the kernel of the idea was what would happen if you took all the components and shrink-wrapped the enclosure to it." The Incredible S is an unusual-looking phone. The front is smart and businesslike but the back is sculpted with square bumps.

And it leads Croyle to expand on an HTC signature design element, the unibody. It's not unique to HTC but it gives a distinctive look. One piece of material creates the bulk of the frame and gives a structure which is light but strong because it replaces multiple elements with one piece. "That inner strength is where the unibody design came from," Croyle says.

Zellweger pulls out a prototype of the Incredible S. It looks like a finished product, with a smooth, solid feel. "You can see the prototype always looks better than the real thing," Zellweger jokes. "When we've made a prototype we give it to Peter [Chou, HTC's CEO]. He'll play with it and come back to us with ideas of how to make it feel better. The Incredible S was very much created to our idea of a design that reflected the inside on the outside, like a muscle car where you have a bulge on the hood to show the engine's power."

A prototype costs up to $10,000, which may not sound much, but there's more than a dozen different versions on the table. They're made in Taiwan and it's a pretty global process overall. The main design centres are in San Francisco and Seattle with a smaller offshoot in North Carolina.

When the hardware is set, the phone networks become involved, with HTC tweaking details as needed. The company works fast – from first prototype to finished product on sale can be as fast as eight months. But the hardware is only half the design story, so the next day I visit the Seattle office – a huge open space with a whiteboard that stretches the length of the room.

Drew Bamford is director of userexperience and works on constantly improving the Sense interface. "HTC Sense now has so many features we're looking at how to hide some to make it easier and more accessible." The key challenge is making the convoluted simple. "Designers have to be annoyed a lot with the status quo to want to invent new stuff," he says. So the latest interface adds extras such as a friend's Facebook status which appears when their call comes in. This way you remember that they're on their way back from a music festival or today's their birthday.

Brainstorming customers' needs is a big part of finding out what matters and I take part in a session. Faster than you can say sim card, complaints pour out, bemoaning the cost of overseas use of a phone, poor signal quality, poor battery life and more. Battery life, no surprise, is the biggest bugbear and has been an issue for many smartphones, including some of HTC's, including the Desire, the company's runaway hit from last year.

It's by far the biggest seller of all HTC's handsets and catapulted the company to a wider audience – now one in five smartphones in the UK is made by HTC and in 2010 the company shipped over 24 million handsets.

Beyond Android, HTC has made more Windows Phone 7 handsets than other manufacturers. Each phone on either platform has a striking physical look and software that's instantly recognisable as HTC.

The company feels like one that's confident about its identity and excited about its future, with lots of ideas up its sleeve. Of course much of that will depend on its patent dispute with rival Apple. A preliminary ruling by the International Trade Commission found HTC has infringed two of Apple's patents. HTC can appeal (and says it will). If it loses it could find it needs to settle with Apple, change the technology in its phones or even withdraw them from the US market, thought to account for half its sales.

Meanwhile, Zellweger sees a move to true smartphones "They'll have more knowledge of us and anticipate our next moves. If the phone knows we usually go to the subway each morning, it'll offer train information as the GPS senses we're heading there." And beyond that? "Well, we're aiming for a non-object," says Zellweger.

"There are screens everywhere today. When they're really ubiquitous, why shouldn't you use a display near you and not have one on your phone. You want the information without having to pull an object out of your pocket." Scott Croyle agrees: "The real question is how do we design that without putting ourselves out of a job?"

The best smartphones currently on the market

For weight

Samsung Galaxy S II

The latest Galaxy S is exceptionally thin and light, but still manages decent battery life. It has an eye-poppingly colourful display and an eight-megapixel camera.

For software

HTC Sensation

HTC's Sense interface overlays great-looking apps and useful programs on the Android smartphone system. The Sensation has a super-fast processor and a large (4.3in) screen.

For design

Apple iPhone 4

The iPhone 4 has the best design and build quality of any smartphone and Apple's iOS software is super-intuitive. When it launched, the phone was criticised for poor signal quality but it didn't stop it selling in huge numbers.

For email

BlackBerry Bold 9900

This new touchscreen version of the flagship Bold is sleek and has an amazingly good keyboard. Combine that with unbeaten security and email delivery features and you can see why BlackBerry is the phone so many executives still have in their pockets.

For battery life

Nokia X7

The X7 will last for days between charges. But it's based on the now-creaking Symbian operating system. In the next months, Nokia launches its phones which use the shiny, powerful Windows Phone system – these will be big news.