Do Airport Speakers work with all iPhone Apps or just Native Music?

I use "JB HiFi Now" streaming service, which is similar to the many streaming services available such as Deezer and spotify.

I read with interest that the new Airport Express released in June 2012 has a 3.5mm socket for external speakers. The Apple info says it will allow me to play music from my iPhone to the external speakers.

I think I know how this would work - in a phone call, I can choose my BlueTooth headset, the inbuilt speaker, or the phone itself as the 'speaker' device to use when I make a phone call, and similarly many applications provide the ability to switch to a different sound output destination.

My question is: are the external speakers available as a music destination for ALL iPhone apps when I'm on the Airport Express's WiFi Segment? Or is it limited to just the apple Native Music app. If so, what apps can I use it with?