Earlier this week, China Times published a rumor that Apple could release an "iPhone Math", a larger iPhone with a 4.8" screen that could compete with "phablets" like the Samsung Galaxy Note. Though the name is particularly suspect, it's possible that Apple would want to get into that product category. Samsung has had some success in the area, and similar products were popular at CES this year.
Russian site AppleDigger.ru has created a mockup of what such an iPhone could look like [Google Translate]. One significant part that the video gets incorrect is that the original rumor claimed the larger phone will come with an 8-megapixel camera, whilst the video says it will have a 12-megapixel camera. Instead, an update to the iPhone is said to come before the holiday season this year, upgrading the lens to 12-megapixels.
Considering the sketchiness of the "iPhone Math" rumor and the lack of any specific claims about how Apple would handle the larger display in iOS, the mockup video should primarily be viewed as a concept giving a general idea of what such a device might look like.