SK Telecom Co., Ltd.  is a South Korean wireless telecommunications operator; it is part of the SK Group, one of the country's largest chaebols.

SK Telecom is South Korea's largest wireless carrier: it leads the local market with 50.5 percent share as of 2008. Since its creation in 1984, the company has evolved from a first generation analog cellular system, to second generation CDMA, then to the world's first third-generation synchronized IMT-2000 cellular system.

SK Telecom also became the world's first carrier to commercialize HSDPA in May 2006.

High Speed Downlink Packet Access (HSDPA) is an enhanced 3G (third-generation) mobile communications protocol in the High-Speed Packet Access (HSPA) family. HSDPA is also known as 3.5G, 3G+, or Turbo 3G. It allows networks based on the Universal Mobile Telecommunications System (UMTS) to have higher data speeds and capacity.

HSDPA was introduced with 3GPP Release 5, which also accompanied an improvement on the uplink providing a new bearer of 384 kbit/s. The previous maximum bearer was 128 kbit/s. HSDPA also decreases latency and therefore the round trip time for applications. 

According to en.wikipedia