Compared to the cost of a mobile phone call, mobile broadband is ridiculously cheap.

Run your calculator across two Vodafone tariffs.

For £25 for a 30 day SIM only contract you can have 700 inclusive minutes with unlimited landline calls, 250 free texts, and unlimited calls between you and three friends who are also on Vodafone.

With each of those minutes requiring 732 kilobytes of bandwidth at 12.2 kilobytes per second, and each text averaging say 30 characters and 0.5 kilobytes, your £25 is effectively buying you the data equivalent of 512 megabytes.

That works out at just over 20 megabytes per £1.00. But let’s say you do have three nominated friends on the Vodafone network, and you also talk to them for an average of 10 minutes each per day, so over those 30 days you consume another 440 megabytes of bandwidth. Each £1.00 would now be buying you close on 40 megabytes.

Good value, you might think. But not when you consider the price of mobile broadband.

There, for each £1.00 you spend, Vodafone will increase your bandwidth allowance to 200 megabytes.

Unarguably, that is even better value. And, not surprisingly, customers intend to continue to enjoy it while they can. Unfortunately, that may not be for long.

According to a report in Computer Weekly, Vodafone's data traffic increased more than tenfold in the year ended 31 March 2008 compared to 2007. However, over the same period, data revenues showed a mere 55% growth.

Similarly T-Mobile also announced a tenfold uplift in WCDMA/HSPA traffic in first-half 2007 compared to first-half 2006. Elsewhere in 2007 operators including AT&T and Telecom Italia Mobile saw at least a fourfold increase in mobile data traffic.

And forecasts for the future anticipate continued exponential growth. Worldwide, mobile data traffic is set to rise by 1,088%, from 162 petabytes (PB) in 2007 to 1,925PB in 2012. However, at the same time, global data revenues will only grow by 77%.

In the opinion of Mike Roberts, principal analyst at Informa Telecoms & Media, and the man responsible for these predictions: “This will push current mobile network costs and architectures to the breaking point.”

His views are shared by such as Analysys Mason, a telecoms and IT consultancy employing 250 staff worldwide, who predict the average monthly volume of wireless network traffic per customer in 2015 will be eight times that in 2008, rising from 56MB to 455MB per month. But, they warn, “if traffic-intensive services are heavily promoted and aggressively priced, total wireless network traffic volumes may accelerate even more dramatically, increasing to almost 30 times the 2008 level by 2015.”

For this reason mobile network operators will need to look closely at their data pricing strategies. Until recently 3G networks have been seriously underutilised, so it has made sense to price aggressively to boost traffic. But, should the growth forecasts prove correct, operators will find themselves forced to make further substantial investment to ensure sufficient network capacity. This they might not wish to do.

Instead, they could decide to increase charges to enhance profits and reduce demand. A few weeks ago at the end of November Telia, the dominant Swedish operator, announced it would do just that.

As a Telia representative put it: “We need to find new models instead of fixed monthly fees, otherwise it will be difficult to run this business.”

Rupert Wood, Principal Analyst at Analysys Mason, was not surprised. He explained: “It may make sense to fill networks with inexpensive mobile data traffic rather than leave them empty, but there will clearly be a point where the economics change. Telia seems to have foreseen this point and is taking steps to protect its investments. The reaction from consumers and competitors will be a critical factor in whether it succeeds.”

Certainly data costs in Sweden have been highly competitive, with Telia offering unlimited usage for a monthly cost of around £20. But some unlimited usage offerings in the UK are not that much more expensive.

For example, for £35 per month Vodafone are offering 700 minutes of talk time, 250 texts, unlimited landline calls and unlimited mobile Internet and webmail, and they will also chuck in a free handset. Other operators have similar offers.

The question is, for how long? Analysys Mason believe there will be sufficient network capacity to meet the predicted demand for the next three to five years, but even that may prove optimistic.

In the meantime, be prepared to see the “network busy” sign on a more regular basis when trying to place a call.