Data calls (including fax) are handled differently from voice calls, so existing mobile subscribers must have their line data enabled (there may be a charge). In addition, only a limited number of phones, from Nokia, Philips and Motorola, support data. Data cards cost about pounds 450 and work in any laptop with a PC Card slot.
Our tests found that the cards worked well with Macintosh and PCs. Installing the data card in the Mac was simple; configuring an IBM laptop to recognise the card took half a day, although this was more the fault of Windows than of the hardware. Some companies offer pre-configured laptop and mobile combinations, and these could be worth looking at. One is Lerryn Data Technology (0161 486 0319).
Some of the most sophisticated personal organisers can also send data. The Psion 3a can be connected to a Nokia digital phone with a Telnote Link (pounds 50-pounds 70). This, however, sends only brief messages via Vodafone's Short Messaging Service. The new Sharp ZR5000 can send faxes and data via a plug-in card.
The cheapest network for data is Orange, which has a standard charge for voice or data calls. This varies between 25p a minute and 14p (excluding VAT) a minute during peak hours, depending on the service package chosen. Orange bills by the second, which can bring big savings, especially with e-mail.
Vodafone's GSM business tariff charges 25p per minute. Billing is in six-second units for data, and 30-second units (after the first minute) for voice and fax. Networks can also offer additional services: Vodafone, for example, provides a fax mailbox as part of its package.
Digital mobile coverage is not quite as good as the analogue networks. Vodafone has the best coverage; Cellnet is slightly less comprehensive, but is catching up; Orange now covers 85 per cent of the UK population.
Subscribers to existing analogue networks have two options: switch to GSM or Orange, or upgrade their handsets.
Manufacturers, including Mitsubishi and Motorola, make data cards for analogue phones. Data is slower, typically 4,800 baud, and the cost of a new handset means this might not be worthwhile.
Analogue cards do have one advantage, however: most can be connected to a conventional phone line.