According to the Korea Times, who cites an anonymous insider, all this derives from the ongoing negotiations reportedly being held between Apple and operator SK Telecom.
The report states that the handset would feature a Qualcomm chip for the LTE-A, more specifically a Qualcomm modem.
The publication writes that from a technical point of view there should be no big obstacle since the iPhone 5 can already manage carrier aggregation technology that offers simultaneous downloads over multiple radio channels.
LTE-Advanced would offer much higher download and upload speeds than current 4G LTE networks.
Source: The Korea Times