The Korean Times has indicated that Apple's fourth-generation iPhone may arrive as soon as April with word that local carrier KT plan to introduce it then.
Apparently KT is in the midst of negotiating with Apple a deal they're both content with and both have agreed they're keen to introduce it 'ASAP'.
What we know about the 4G iPhone at this stage is that it'll boast an OLED touchscreen and have support for video chatting (suggestive of having a secondary camera aboard). Also apparant is a superior main camera, better performance with a dual-core processor and superior graphics core.
Talk of a removeable battery has also come about, but that could be nothing more than wishful thinking.