And instead of using the phones to clinch that all-important business deal, many fleet drivers only used them to chat to their peers about work.
Saul Jeavons, a principal consultant in investigations and risk management at the Transport Research Laboratory (TRL), said recent laws banning the use of handheld mobile phones in cars had not made any difference to trade for most firms.
Speaking at a fleet safety forum staged by road safety charity Brake, Jeavons said companies faced a real dilemma when they tried to ban calls to mobiles when staff were likely to be driving, while expecting their team to always be available.
Commenting on the law, which was introduced in December, Jeavons said: 'The quality of business will not deteriorate – mobile phones were often used by employees to make calls to talk about sales won or lost. Some companies make it a disciplinary offence to answer the phone when driving. It is difficult to enforce, though.'
The TRL is conducting new surveys into mobile phone use for the Department for Transport (DfT).
Drivers are being checked on a cross-section of highways from minor roads to motorways, and results are likely to be published before the autumn.
Staff count the number of vehicles whose drivers are seen to be using a hand-held mobile phone. In the latest surveys, observers use electronic equipment that detects the radiation emitted by a mobile when it is in use.
In a statement, the DfT said: 'The numbers are used to calculate the proportion of drivers using either a hand-held or hands-free mobile phone.'
The TRL has conducted mobile phone surveys for the DfT since October 2000.
Jeavons said at the conference that TRL research for the Direct Line insurance company showed that braking distances increased when drivers were using mobile phones.