The three companies will supply base stations and other transmission equipment, considered a core technology in the commercialization of the 5G network, South Korea's No. 1 mobile carrier said.
SK Telecom said it ruled out Chinese tech giant Huawei Technologies Co. in the final decision.
"SK Telecom selected the aforementioned three companies for the realization of the 5G ecosystem and world-class service quality," the company said in a press release, adding that technological capability, as well as financial factors, were considered.
SK Telecom said earlier it will start commercial operations of its 5G mobile network in March 2019. 5G data transmission speeds are 40-50 times faster than the existing 4G network or long-term evolution (LTE) and are expected to open a wide range of new business opportunities for the communication service sector.