Right now, there are some concerns with iPhone fragmentation as some users get their hands on the Verizon iPhone.
This came up when Telenav announced recently that they had released their GPS App for the Verizon iPhone. It's identical to their App released for the AT&T iPhone with the exception of it working on Verizon's phone.
Long story short, the new App is designed to work with the new iPhone hardware. One report says that this can many App makers may be forced to develop different versions of their software for users on different carriers. The iPhone is popular on both carriers already, and both are markets that developers would be wise to cater to.
It will be interesting to see how this works out in the future.