Some are already being charged as much as £150 for the removal and repair of a single kit at the end of the car's contract period, experts warn. And this sum could multiply to hundreds of thousands of pounds per annum for a large fleet.
Small to medium area repair technique expert Dent Wizard warns there is a huge variation in prices for the same work carried out at disposal time in the industry.
It charges what it terms a 'fleet-negotiated' price and one which also includes the delicate removal of the kits so that they can be re-used in a different vehicle.
But research has shown that much larger sums are being charged that could catch out fleet decision-makers, who could face a bill for more than £1,000 after de-fleeting 10 cars.
Dent Wizard International UK managing director Quintin Cornforth said: 'Hands-free mobile phone kits have been installed in company cars and vans for years.
'But, since the introduction of the legal ban on the use of hand-held mobile phones in December last year, many fleet managers have been busily installing hands-free kits into company cars for their executives.
'In many cases, this involves drilling three small holes into the vehicle dashboard for the screws that fix the kit. When the car is returned at the end of its contract, or otherwise disposed of, the kit is removed and the holes repaired in order to maximise the vehicle's resale value.'
If this is not done, the vehicle might fail to meet its set residual value, while contract hire and leasing companies or motor manufacturers are bound to charge for making good the damage to their vehicles.
Cornforth added: 'The damage caused by the installation of hands-free kits hardly qualifies as fair wear and tear.
'The problem is that fleet managers are often totally unprepared for the sometimes high costs involved here. They need to factor in the price of removing the kits and repairing the damage into their end-of-contract costs for each company vehicle and, in the process, would do well to consider the savings that can be achieved by employing SMART repairs.'