In the old days, a 999 call would light a special lamp on an operator's switchboard and she (always female, then) would ask for your name and address and pass the call to the relevant emergency service.

Nowadays, emergency calls go to a small number of call centres before being passed to the local emergency services and the system automatically uses the phone number to look up the address.

This all works pretty well when the call is from a residential fixed line or a call box. Calls from most business lines are fine too, but if the contact is from a large corporate with a private network, the call might break out a long way from where it originated and indicate the wrong location.

Corporates should, therefore, ensure that they program their networks in accordance with the advice of the public network provider.

Problems can also be caused by calls from mobiles and calls crossing networks owned by different operators. In the future, systems will also have to be set up to properly handle videophone and IP telephony calls.

But let's consider the mobile case a bit further. At the moment, the mobile operators provide the best location information they can but this is only accurate in urban areas where cells are smaller.

As well as indicating which base station antenna is in use, the network also identifies roughly how far the mobile is from the antenna. This system can provide the location to a few hundred metres in cities, but in rural areas it may be far less accurate. Co-operative technology on the mobile can improve accuracy but the facility is not yet ubiquitous. It's worth noting that 3G networks will be better than GSM in terms of accuracy, but will still need co-operation from the mobile devices.

Over the last few years, the cost of Global Positioning System (GPS) technology has plummeted to the point where it can be included economically in mobile handsets. Unfortunately, GPS is not a complete solution because the signals are too weak for it to work indoors. GPS receivers also generally take a couple of minutes to obtain an initial fix because of the need to acquire the weak satellite signals. This is far too long for emergency situations.

However, the GPS people have designed Assisted GPS (A-GPS). This provides the mobile GPS receiver with up-to-date information about the satellites and shortens the acquisition time to a few seconds. This is a great improvement but does little for the indoors problem.

But a recent collaboration between Infineon and Global Locate has resulted in a GPS chip called Hammerhead, which does the acquisition and tracking calculations in parallel; this allows it to start up almost instantaneously and integrate the signal for much longer yet still be responsive. And the makers claim that it works indoors thanks to the boost in sensitivity.

As operators want to provide lucrative, location-based services, besides those needed for emergencies, I think this type of technology will soon be widely deployed.