The London hotspot's Latin lesson

As Wi-Fi coverage rolls out over the Square Mile, the numbers look bad for existing mobile operators

The City of London is no stranger to hotspots. Boudicca burned it to the ground in 61BC, and the place has combusted with some regularity since. The Cloud's new citywide Wi-Fi system will be somewhat kinder to the buildings — but it could do more than singe the beard of the mobile network operators.

Competition is the key to effective new services. It's certainly the way to break down some of the barriers to mobile data. Access in the London hotspot will cost around £5 an hour — which may sound steep, until you do the sums. An hour's worth of Wi-Fi data would cost £360,000 under Orange's top roaming data tariff, to pick on a favourite offender. If you pay a typical £25 a month for unlimited hotspot use, you could download data for which Orange would change £267,840,000 — over a quarter of a billion pounds. This ten million to one ratio may be the biggest disparity in the history of computing: it's now going to be glaringly obvious to London's top financiers.

Even on the mobile networks' home turf of voice, the advent of city hotspots is bad news. Wi-Fi chips are becoming cheap, capable and low power enough to go into handsets where Bluetooth went before, and there is no shortage of companies offering VoIP clients on mobile platforms. As the standards for interconnecting all these components evolve, the pressure for revolution builds

The mobile operators know that the ground rules are changing. They know that they'll no longer be able to charge what they like for outdated services, that both voice and text messaging revenue will approximate to zero soon enough. Huge numbers of nimble competitors will swarm from the hills like Iceni warriors, eager to use the empires' massive legacies of infrastructure costs and sclerotic billing systems against them.

It's still possible for the networks to prepare their defences. Fixed-cost voice, text and data will help. A rapid and ubiquitous deployment of the next generation of instant messaging systems will help create communities with a strong motivation to stick to their suppliers.

And it's still possible for them to get it wrong. Boudicca rebelled against the Romans because the procurator of Britain, Catus Decianus, decided to get greedy. Any network operator which still thinks it acceptable to have a tariff where a £1bn bill can be run up by one phone in four months may like to ponder his fate.