Officers claim it is a dangerous activity and a major factor in many crashes which result in death or serious injury.
Motorists are warned that they could be fined up to £1,000 if stopped by police for using a mobile phone while driving.
The campaign is being co-ordinated by South Wales Police but involves all four Welsh police forces.
Sergeant Nigel Whitehouse, Community Traffic Safety Officer, said the problem had reached "epidemic" proportions.
"Motorists should remember that it is a highly dangerous activity and a proven killer.
"There are a number of collisions in which people have been killed or seriously injured throughout the UK in which the use of a mobile phone has been attributed as a major factor."
Fatal consequences
In 1996, eleven-year-old Rebekka Hudd died after she was hit by a four-wheel drive vehicle near her home at Pucklechurch, near Bristol.
David Powell, who had been using a mobile phone at the time of the accident, was fined £250 and given six penalty points after he admitted careless driving in relation to Rebekka's death.
In February 2001, a lorry driver who was using a mobile phone to send a text message to his girlfriend when he hit and killed a pedestrian was jailed for five years.
Paul Browning from Surrey was convicted of causing death by dangerous driving when his lorry struck pedestrian Paul Hammond in a lay-by on the A13 in Essex, in June 2000.
In November 2001, police condemned a one-armed man from Swansea who was caught drink-driving after driving through a red light while using a mobile phone.
Stuart MacNamara, 34, was given an 18 month driving ban and was ordered to pay fines and costs totalling £450.
Heavy penalties
Under current legislation there is no specific ban on using mobile phones while driving.
But police say that motorists could be summoned for driving without due care and attention.
The offence carries a fine of up to £1,000 and three penalty points.
Alternatively, drivers could be given an on-the-spot fine of £30 for not being in proper control of a motor vehicle.
Police are urging motorists to keep their mobile phone turned off during long journeys to avoid distraction.
They advise people expecting an urgent call to stop safely at regular intervals to check their answer phone.
In January, nearly 50% of drivers who took part in an RAC survey admitted using mobile phones in their cars, usually with a hands-free kit.
But 42% said banning mobiles should be the government's priority for cutting accidents, and 31% wanted better policing of the use of phones in cars.
The UK Government says it has no plans to introduce legislation on the use of mobile phones in cars, but has the matter under review.