I really don't mean to be rude but You'll drive yourself crazy trying design for iPod/Phone without owning one & testing.
Wait till you own one.
You are quite correct...
There are two ways to design:
1) Create a complex Filemaker database on your local computer and then go crazy trying to find out why it acts up on a remote host, IWP, Go, PHP, etc.
2) Start from scratch and design a file for the specific use intended, Local, Remote Host, IWP, Go, etc.
I have tried to help people understand the concept of creating a new mindset for developing for each of these environments but it is sometimes difficult for them to understand and to get past the glowing advertisements and into the reality.
So, I am starting from scratch (24 years consulting and Filemaker experience) within the design parameters I have set... :) Unfortunately this list stops at 10 years in the about me....
I have read the faqs and know what to avoid and am just working on layouts etc that don't really require using the critter. I am also avoiding the problems folks encounter when they try to use their magnificient Filemaker/local layouts in different environments such as IWP or hosted remote or GO. I am doing this by designing specifically for GO, as if I used a new GUI file to address the db. Of course without the phone there are areas I know not to attempt and these must wait as you point out.
I know that using dial needs the iphone and that Open URL will switch to the built in browser, etc. Plus snagging photos, signatures, etc.
As you can see from my layout, I have designed it to fit the 320 x ? required for the iTouch and iPhone. For now I am dealing with creating a navigational system just for the iPhone layout and for that the layouts work just fine.
Actually I have discarded that fixed button idea and am presently creating menu sets using a portal and a global for choosing between Main Menu, Address Menu, etc. This simplifies my design work and I only need one layout rather than 20 or 30 for a menu system, or unlimited menu sets as some might say.