Over ten thousand mobile phone users have been taken in by text messages sent randomly to their mobile urging them to call a phone number, which later turned out to be charged at premium rates.
Four UK firms have each been fined between £1000 and £10,000 for running the scam.
Two more firms are still being investigated by the premium phone rate regulator, the Independent Committee for the Supervision of Standards of Telephone Information Services (ICSTIS), which hasn't ruled out claims that the same individuals were involved in more than one case.
SP Services of Sheffield was last week fined £10,000 for sending a text message urging callers to ring one of five different numbers. The text messages contained no information of premium rates, and were along the lines of "please call me on 0900 1234567, urgent".
When the user rang, they were greeted by either a recording of an engaged tone or a tipster phone service, and charged 50p.
Wellbourne Services of Manchester and Mega Mobiles of Leeds were also fined for advertising numbers linked to recordings of engaged tones and charging 50p a call.
Sporting Voice of Harrogate used the same technique to drive callers to its practical joke line, charged at £1 per minute.
Outraged users only discovered the hidden costs when they received their phone statements.
Rob Dwight, a spokesman for ICSTIS, said: "Using text messages seems to be the latest idea to make money. There can be no excuse for playing recordings of engaged tones, which are obviously used only to generate revenues by persuading people to call lines more than once."
Dwight said the regulator had now handed its files over to trading standards officers who will decide whether to press fraud charges against the operators.
He also said ICSTIS was currently taking legal advice on whether the process of randomly sending messages was illegal.
However, users are unlikely to get their money back as ICTSIS can fine operators of premium rate services but does not yet have the power to force refunds to consumers. Dwight said that ICTSIS was reviewing its rules so that future victims could apply for refunds.
The regulator also has the power to ban individuals from running premium phone rate services in the future.
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