At just 20 years of age it is undeniably a relic from another age, already long consigned to the past.

But, clunky as it may be by modern standards, the IBM Simon has an important place in history - it was the world's very first smartphone.

Tomorrow marks the anniversary of when the Simon first went on sale, and in October it will get a new lease of life when it goes on display as part of a permanent exhibition on the history of communication and information technology at London's Science Museum.

The phone was developed by computer firm IBM and the American cellular company BelSelf. It was called Simon because it was simple and could do almost anything you wanted.

Charlotte Connelly, the content developer for the exhibition, said it was initially marketed around the idea of the game "Simon says".

"The marketing was that it was so simple that it could do anything you instructed it to," she explained.

Compared to today's smartphones it was incredibly basic, but in 1994 it was far ahead of its time.

The Simon, with its green LCD screen, had a stylus with touch screen technology.

Software allowed users to write notes, draw, update their calendar and contacts and send and receive faxes, as well as allowing calls. It even had a slot for cartridges that were primitive "apps".

But at around nine inches long (23cm) it was also about half the size of a house brick. It had an aerial and its battery lasted just an hour when making phone calls.

It also weighed the same as half a bag of sugar.

"It was half a kilogram (1lb) - you wouldn't want to carry it too far," Ms Connelly said.

Nevertheless it was revolutionary, combining for the first time attributes of PDAs - those personal digital assistants beloved of businessmen - with mobile phone technology.

"The Simon was the first device that took these two items and put them together in a single package," Ms Connelly said.

"It could do all the things in a PDA and it also had fax capabilities and could do email, though it had to be synched to a computer to do that.

"That is why we are calling it the first smartphone, even though that phrase first came along much later.

"It has all the components of a smartphone, including a slot in the bottom to insert different applications, such as mapping ones, spreadsheets and games.

"So it was really a forerunner to the iPhone."

Available only in the US, it initially cost 899 dollars when it first came out. Around 50,000 handsets were sold, primarily to business people.

The one owned by the Science Museum was bought on eBay for an undisclosed sum.

"I asked the seller what it was for and it was owned by a project manager for a construction firm," Ms Connelly said.

"He really liked the fact that his co-workers could fax him technical drawings, he could sign them off while on assignment and send them back to them, rather than having to have papers all over the country."

But the Simon was to have a short lifespan, partly because it was so far ahead of its time.

Ms Connelly said: "It didn't make a massive splash.

"It was only available in the States, and was only marketed there as well.

"It was just early adopters that knew about it at the time - it wasn't something that everybody in the country craved to have.

"There was probably an element of lack of demand of people not buying into it, but it was only a few years later that the Nokia 9000 Communicator came along."

The price was dropped to 599 dollars after six months because it was commercially unsuccessful, before it was withdrawn completely. Not many are left in circulation now because IBM recalled it.

"First of all it was very expensive," Ms Connelly said as she explained its failure.

"Secondly, the battery only lasted an hour in talk mode, so it wasn't very practical, and third there was no mobile internet.

"A lot of the things we want our mobile phone to do today just weren't possible because the connectivity wasn't there."

She added: "It has got all the fundamental things there, but honestly, would I like to carry it around in my pocket? No, I wouldn't. You can see the potential but it didn't really deliver.

"But really it was a brilliant idea that was just a bit ahead of the technology.

"All the bits of the jigsaw puzzle weren't quite in place. It was too far ahead of its time."

But while it is already a relic, most handsets now probably lost in dusty garages or forgotten in bottom drawers, the IBM Simon left an indelible mark on the world of mobile technology.

"It is the first smartphone, " Ms Connelly said. "It is the first time these crucial components were brought together in one single device, and although it wasn't a commercial success it was a pioneer."