According to a post on The Register, a UK company called Blue Sky Positioning has announced it has managed to cram a functioning GPS device onto a normal mobile phone SIM card.

BlueSky Positioning CEO Risto Savolainen said: "We are only allowed [by the GSM SIM standard] to draw six milliamps, which was a challenge."

One of many, it would seem. When it comes to picking up the GPS signal Blue Sky Positioning had a novel approach: "Most antennas are designed in free space, to have nothing around them. We started out knowing that there would be metal all around us. That's our secret - how the antenna works, but when we take away the battery, take the SIM out of the phone, the signal is no longer there."

The SIM is of standard size and shape, though wouldn't pass the full ISO tests for flexibility and robustness.

The service is actually an implementation of A-GPS (Assisted GPS), so some of the functionality comes from off-SIM, but it's still an incredibly impressive piece of shrinkage.