The investigation was prompted by complaints from consumers
A near-record fine has been handed out after consumers were thrown by a recorded telephone message that caused them to call a higher rate number.
Regulator Phonepayplus has levied its second-highest fine of £200,000 following the investigation.
Thirty-two people complained after receiving an unsolicited phone call which they thought was somebody trying unsuccessfully to talk to them.
It prompted them to call back on an 070 number which charged at a higher rate.
The adjudication from Phonepayplus said that unsolicited calls were made to residential, business fixed-line, and mobile phone numbers using automated calling equipment.
Recipients said that the call lasted for about five seconds, when they heard a man's voice saying "Hello, hello, can you hear me?" before the call ended.
"This prompted consumers to return the call while being unaware of the higher-rate charges," the adjudication said.
The regulator's tribunal ruled that its code of practice had been breached and fined service provider Jack Barnard Telecom Services, of Epping in Essex, £200,000.
A Phonepayplus spokesman said this was the second highest fine, after new rules increased the maximum fine available.
Opera Telecom was fined £250,000 after viewers lost an estimated £20m in phone-in quizzes on GMTV.
Jack Barnard told the BBC that he intended to appeal against the fine, which he said was higher than the income generated by the calls, on a number of grounds.
He did not want to go into more detail until he had seen the full adjudication.
These 070 numbers are used by businesses which spend time on the road. They are called "find-me-anywhere" services and cost up to 50p a minute to call from a landline number or possibly more from a mobile phone.
More cases of alleged 070 number breaches are expected to be considered by the tribunal following this test case.