Kiss 100 FM has been fined £175,000 by media regulator Ofcom - a record penalty for a commercial radio station.
The fines were for 10 complaints about Bam Bam's breakfast show
Ofcom punished the London station for "numerous and serious breaches" of broadcasting codes on its breakfast show between April and November 2005.
They involved prank calls where consent was not sought from the "victims" and inappropriate material aired when children were likely to be listening.
Kiss FM said it accepted the findings and apologised for any offence.
The award-winning breakfast show was presented by Bam Bam and Streetboy.
Bam Bam left Kiss FM in April and Streetboy continues to work at the station on a different show.
Ofcom said one of the prank calls was "the most serious case of unwarranted infringement of privacy it had heard".
The call was made to a member of the public, Mr R, who mistakenly left a voice message on Streetboy's phone, believing he had dialled his human resources officer.
Mr R had recently been made redundant and was hoping to discuss redeployment opportunities in his company.
Instead, he was called by the presenter, who impersonated the human resources officer and chastised Mr R for wasting his time.
Even after Mr R's distress became apparent, Streetboy told him "to go and flip burgers or something", Ofcom said.
When the call ended, the presenters were heard laughing and acknowledging that Streetboy was "dealing with this guy's whole future and career".
Kiss FM's parent company, Emap Radio, described the decision to broadcast the pre-recorded item as "inexplicable" because even the presenter admitted it had gone too far.
Emap Radio agreed that the item was a "horrible intrusion into someone's privacy... it was also extremely bad for the radio station".
In its ruling, Ofcom said: "The broadcast was devoid of any justification of public interest and could have had a serious effect on the individual concerned."
Taking into account a similar complaint about another prank call, Ofcom imposed a fine of £75,000.
The other breaches of the broadcasting code centred around the use of inappropriate language, including swearwords and sexual references, during the breakfast show.
Ofcom upheld eight complaints, saying that "for a substantial period of time the compliance of the show was evidently not under proper control".
This resulted in a further fine of £100,000, for the "serious number" of "repeated breaches" made by the station.
Emap Radio admitted it could not defend some of the material that had been broadcast and said its procedures were "not up to spec" at the time of the broadcasts.
The company said presenters and producers at the station had been brought up to speed on the broadcasting code, while new complaints procedures have been put in place.
Kiss FM managing director Bill Griffin said the station tried to "push the boundaries whilst engaging the capital's biggest young, urban audience".
"We accept that we can sometimes unintentionally overstep the mark," he said.
"We have made every effort to prevent a reoccurrence."