UPC, Vodafone, O2 and Eircom have pleaded guilty to breaching the Data Protection laws.
The charges related to the making of unsolicited marketing phone calls and sending unsolicited marketing messages.
The companies were ordered to pay almost €15,000 in fines between them.
UPC was convicted of the largest number of offences and received the biggest fine.
It pleaded guilty to 18 counts of breaching the Data Protection Act in relation to four separate complaints, one of which the Office for the Data Protection Commissioner said was one of the most serious cases every to come before it.
The Dublin District Court heard that after a letting agent had cancelled 56 accounts with UPC the company attempted to contact one of their employees 225 times in a period of less than three weeks.
When they got through she had asked them to stop calling but the contact persisted. She then emailed them and asked them to remove her mobile number from their records. They said they would but only if she gave them a landline number instead.
Assistant Commissioner at the Office for Data Protection, Tony Delaney said that the women felt like she was being harassed and that it took UPC a number of weeks to resolve the issue.
The company were also convicted of making several unsolicited calls to three other woman who had asked not to be called for marketing purposes.
Judge Brigit O'Reilly said evidence suggested that UPC had been less than fully co-operative in resolving the problems and in light of their previous conviction for breach of the Data Protection Act she was imposing a fine of €7,100.
Vodafone was convicted on five counts of breaching data protection legislation after one of their customers received four unsolicited marketing phone calls and another had received several marketing text messages.
Vodafones Irelands Director of Regulatory Affairs Julian Hayes told the court that the company accepted the breaches and apologised for the annoyance caused saying the company did not intend to aggravate its customers.
He said there had been issues with third party companies who work on behalf or Vodafone and they were currently reviewing their relationship with these vendors.
They were fined €3,850.
Eircom pleaded guilty to one charge of breaching Data Protection laws after a member of their door to door sales team phoned a former customer who had been told his name had been removed from their marketing list.
The Judge applied to the Probation Act and ordered to donate €2,000 to charity.
O2 also pleaded guilty to one charge of sending an unsolicited marketing text message to a customer three years after the customer had contacted the company asking not to be sent such messages.
The company claimed that the message was sent due to a technical discrepancy in their data warehouse.
The Probation Act and a fine of €2,000 was also imposed
The Office for the Data Protection Commissioner said it was very satisfied with the outcomes of these cases.
It said it sent a strong message to companies large and small that people care about their Data Protection rights and that the laws need to be complied with.