Recent rumors suggest the next iPhone will rock a bigger screen, moving from its current 3.5-inches up to 4-inches. Though users may be clamoring for a larger display, this new hardware could cause problems for developers who will have to design for several screen sizes. GigaOM talked to several iOS developers about the potential for fragmentation and discovered most are cautiously optimistic about this change.
The overall consensus is that Apple will provide tools to make the transition from a smaller to a larger display as easy as possible for developers. Many point to the original iPad and the retina iPad as examples of how Apple has handled this transition in this past. If you're interested in the developer's individual responses, you can read them on GigaOM's website.