Can I use my iphone and pandora with airport express to play on my home speakers?

Possibly. With iOS 4.3 and later, you can stream audio from third-party apps, like Pandora Radio, installed on your iPhone ONLY if the developer for the app has added AirPlay functionality. I did a quick review of this app from the Apple App Store and it did not mention having this feature.

I can confirm that pandora works with iPhone and communicates with AX units

Thanks for verifying that it does!

With the caveat that it can only stream to on AX unit at a tinr