You thought junk mail was bad? Now we have the mobile phone equivalent and it’s even more annoying and intrusive.

It’s known as “slamming”, and instead of stuffing your letterbox with mail, perpetrators bombard people with calls, trying to sell them mobile phone contracts.

“Slammers” frequently offer handset upgrades and free call time but their aim is to switch people to a new network provider. They work in return for commission from mobile phone companies but the techniques they use are sometimes aggressive and misleading.

Customers are approached at random, and no explanation is given by the caller as to how their phone number was obtained. In some cases customers have unwittingly switched provider or signed up to an expensive long-term contract they never wanted.

Some people have received as many as eight slamming calls a day. The Sunday Times recorded a call last week — this is an excerpt of the conversation. Caller: “Hi. I’m calling because we’d like to offer you a free upgrade on your mobile phone.” Sunday Times: “Oh really?” Caller: “Yes. If you are coming to the end of your contract we can give you a new phone, free call time, free texts and video messaging. Sunday Times: “Where are you calling from?” Caller: “We work with the 3 network and we also do Orange deals.” Sunday Times: “But I’m with Vodafone, how did you get my number?” Caller: “It comes through to a database in our Cardiff network.” (In fact the numbers are randomly generated by computer and the call centre staff have no idea who they are phoning.) Sunday Times: “What’s your name?” Caller: “Jade.” Sunday Times: “And your surname?” Caller: “Why do you want to know that?” Upon further investigation it transpired that Jade works for Communications Direct in Cardiff. On its website this marketing company boasts that it is one of the largest and fastest-growing communications sales companies in the UK, and claims to sell a mobile phone contract every 40 seconds.

What the website doesn’t mention is that earlier this year O2 began legal proceedings against it for allegedly trying to sign the network’s customers to rival providers while giving the impression its staff were from O2. All the major mobile phone networks — Vodafone, Orange, O2, 3 and T-mobile — do deals with third-party marketing companies to sell their services.

These companies receive commission in return for winning new customers to the network. Orange, for instance, has arrangements with about 2,500 such companies. But the big five insist they do not sanction the tactics used by some slammers (although it’s legitimate to ask why they prefer to pay commission to outside companies rather than make the calls themselves).

In a climate in which competition between providers is intense, and with the mobile phone market now worth £13.1 billion in the UK alone, it appears that unscrupulous and occasionally underhand methods are being overlooked.

Ofcom, the telecoms regulator, says it has received a growing number of complaints about slamming in the past six months but is powerless to act as the companies involved are not mobile phone providers, and are merely resellers. Ofcom defines slamming as switching customers from one provider to another without their consent but the term has been expanded in common parlance to describe aggressive unsolicited calls by telemarketing firms. recently took legal action against Landmark Marketing Services, aO2 Welsh telesales company, and won a £500,000 out-of-court settlement. It says it is currently investigating a further 60 companies after receiving about 100 complaints a month from its customers about nuisance calls. “This is a highly worrying practice,” spokesman. “It has become prevalent as competition has increasedsaid an O2 within the industry.” is not the only operator taking action. Last month Orange terminatedO2 working relationships with 20 dealers who it said had misled customers. Other networks remain more laid back, though: a 3 spokesman said he didn’t believe the practice was common.

When The Sunday Times spoke to Communications Direct last week, a spokesman said: “Our company satisfied every regulatory rule. Every call is rigorously checked. If something inappropriate has been said [by a salesperson], immediate action will be taken.”

In the conversation recorded by The Sunday Times, it is true that the caller from Communications Direct at no time claimed she was calling from Vodafone or another mobile phone provider (she said she was working with the 3 network and Orange) and did not attempt to switch our phone to another provider. Communications Direct also said it would vigorously . “On defend the action brought by O2 the evidence available to us, we are will fail.” confident that O2 People who have received a slamming call can contact the Office of Fair Trading (OFT) if they want to register a complaint, and have seven days to terminate any unwanted contract, according to OFT rules.

For those who don’t want to be called at all there is a way to stop slammers contacting you, and it’s supposedly more effective than putting a “no junk mail” sign on your letterbox. You can register your mobile number at a website run by the Telephone Preference Service (www.tpsonline.org.uk). In theory, after 28 days this should stop all UK-based telemarketing calls, though it won’t stop unsolicited text messages.

The best deals

Mobile phones and their tariffs are many and confusing, but our tips may help you find the best deal

- Do you want a slim fashion phone or feature-packed smartphone? See InGear’s recent rundown for inspiration: tinyurl.com/yqm43s

- Visit www.mobilechecker.com to compare tariffs from every network and for virtually every handset

- Big chains often offer cheaper deals online. The Carphone Warehouse’s subsidiary www.e2save.com regularly beats its better-known parent on price

- Make sure you are happy with details such as the length of a contract; you’ll get more free minutes and texts with an 18-month contract, but that ties you to one phone for longer

- Be wary of complicated cashback deals. These can appear to be better value than they are, so ensure the actual monthly payments are properly explained by the seller

- Don’t be afraid to haggle once you’ve decided on your tariff and phone. Phone companies are so desperate for custom they’ll give away extras

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