In order to put backtrack on the iPhone, it would first need openiboot, in order to boot into a linux OS. Currently only the iPhone 2G, iPhone 3G, iPod Touch 1st, and 2nd Gen have supported OpeniBoot. Everything else is completely experimental. If you're interested, you can visit
http://www.idroidproject.org/wiki/Main_Page
Basically, OpeniBoot was developed when people were putting Android on iPhone hardware. Once OpeniBoot is supported on a device, then the Backtrack image could be tweaked to be installed on there.
Also, there is a way with a jailbroken iPhone to SSH into your backtrack computer, if that's what you were implying for taking backtrack with you...otherwise, you can install metasploit and nmap and other tools on a jailbroken iPhone just by itself and run them in terminal emulator, except not a whole lot is supported.



