It really depends on each individuals preference and design workflows to choose the design app that want to design for mobile app. Both Photoshop and Fireworks have the design capability to design beautiful icons and user interface. You can first do a search on Dribbble to find works of mobile apps of people working on.
I know there are designers using Fireworks to design iOS apps. Here are some examples
http://cir.ca/
http://dayoneapp.com/
I will definitely prefer Fireworks as its workflows are much better to work with and it is more towards screen designs. If you have explored the vector editing and used its path panel for boolean operations on vector shapes, you will know Fireworks has more to offer to a designer.
The fact that i can have one page on icon design and another few pages on the app interface design is really cool. I am able to work on every assets i am working, pull in screenshots ideas and work on it in a single document is very powerful. One of the most important workflow a designer will need is updating the design element on 1 page and see it updated on other pages instantly.
I also do prototyping and the use of pages, slices and hotspots enables me to vision and interact to see how the app will work too and then export the designs out for client to see using the PDF export. That is such a time-saver to me as well.
