It is most often referred to as tethering. Using your phone and it's 4G service as a WiFi HotSpot where other WiFi devices can connect and share the S3's 4G service. Tethering is carrier dependent. There is usually an additional monthly charge of $20 plus to tether. Check your carriers website for tethering or hotspot for information.
There are also 'illegal' methods to tether with a smartphone, but you run the risk of having you cell service canceled or being charged with theft of service.