This paper presents the results obtained from the survey research of existing accounting information systems of telecommunication operators in Croatia regarding regulatory challenges of today's telecommunications market. The questionnaire was sent to all registered operators, providing fixed and/or mobile telephone services, but only six of them responded and filled the questionnaire. This survey research of existing Accounting Information Systems (further in text AISs) of telecommunication operators in Croatia shows that the majority of AISs are small and limited. It is due to the fact that Croatia has one SMP operator who has most of the infrastructure in its ownership and as such has large and complex AIS while the vast majority, who rent most of the infrastructure, have small and limited AISs.