This study examined the discourse structure of telephone enquiries used by Malaysian English as a Second Language (ESL) speakers in simulated service encounters in the business context. The specific objectives of the study were to identify the structure of the opening and closing exchanges of the telephone conversation and the structure of the service encounters. Oral interaction data were collected from 28 ESL speakers from an English for Professional Purposes course participating in paired role play situations involving restaurant reservation, hotel holiday package and products. The results showed that only three out of 14 interactions had the obligatory Sale Request ^ Sale Compliance ^ Sale ^ Purchase ^ Purchase Closure structure of service encounters found by Halliday and Hassan (1985). For the telephone conversation, only half of the openings followed the Greeting, Identification and Statement of Availability sequence but 12 out of 14 closings had the Preclosing ^ Leavetaking sequence taught in the course. The discourse structure of the telephone-mediated service encounter in the business context was found to be difficult to master for most participants in the study.