Here is a video with a concept render on how a 5.7-inch iPhone phablet could look. Oh, and of course it runs iOS 7. Personally I must say that this is something Apple should do. Even I personally could be thinking of buying that one. If Apple fixes iOS 7 to be able to share to the services I want, and be able to set default apps and so on..
The rumor says that Apple will do such device, but personally I have a hard time believing that they will though.