Consumers are being misled by confusing marketing material for mobile phone deals, officials warned.
Trading standards received 1,167 complaints on the issue during the first six months of 2007 from people in the central England area.
Its investigation found nearly twothirds of mobile phone adverts failed to state the minimum term contract period or the monthly line rental charge.
Nearly a quarter of the adverts were misleading in some way, trading standards officers found.
Finding out the cost of buying and using an advertised mobile phone deal was difficult in nearly two-thirds of cases. One problem was that in-store publicity brochures were not userfriendly enough, officers said.
Scant information in shops about mobile phone deals also made it difficult to work out the cost without asking sales staff.
Trading standards operations manager Anita Hunt said adverts for mobile phone packages were generally uninformative.
"Anyone wishing to buy a mobile phone should be able to make accurate comparisons from the information supplied in advertising and marketing material. They should not have to visit every retail outlet and ask staff directly," she said.
"It is clear from our investigation that current legislation and codes of practice do not adequately regulate the sale of mobile phone packages."
In some cases trading standards officers posing as shoppers thought shop staff were pushy and forceful when persuading them to sign a mobile phone deal.
Central England Trading Standards Authorities (Centsa) wants a single format to be used for all in-store information about mobile phone deals. It has sent details of its findings to Ofcom and the Office of Fair Trading.
Centsa wants the code of practice for the sales and marketing of mobile phone network subscriptions to be beefed up. Its findings were based on a survey carried out by 22 Trading Standards officers.
They examined 52 mobile phone adverts found in the central England region and visited mobile phone stores.
Their aim was to find out whether shoppers could work out the true cost of buying and using a mobile phone without any help from sales staff.
A spokesman for the Advertising Standards Authority (ASA) said: "We have not been deluged with complaints on this issue. We are not getting the same sort of feedback from consumers as Trading Standards have found. If there appears to be a problem in a specific sector then obviously the ASA will look into it.