False diagnosis?
I have googled the issue, and while there may be more cause for the same error message, in my case CLEARLY it's not any of the reasons people claim are the reason:
a) in
http://discussions.apple.com/thread.jspa?messageID=8085756 the "answer" Apple iTMS maintenance. Not the case I have this issue 24*7*365
b) others suggested to reauthorize the iPhone with iTunes, wrong again.
c) there were other suggestions, like hard-reboot the iPhone, etc. which again are all wrong.
Here is what I have figured out: if I turn off WiFi, it works over EDGE. If I go to a public hotspot I know in a nearby coffee shop, it works over WiFi.
In other words, there is an issue with CERTAIN, but not all WiFi networks.
I have searched (to no avail) if the mobile version of the iTunes store uses different ports or requires otherwise specific firewall settings. Couldn't find anything. Regular services (Safari, Facebook, Skype, VNC, ssh, etc.) work from iPhone and Mac, iTMS works from Mac, but not from iPhone when on my home WiFi network (Apple AirPort plus ZyWall gatway).
My suspicion is that the app tries to create a tunnel, and since some ISPs already create a tunnel to connect their clients into their backbones, there might be issues with tunneling a tunnel, VPN passthrough, or other such things.
Since Apple doesn't seem to know what's going on, and since most users seem to try voodoo rather than analyzing this problem in a more scientific way, this is likely to stay with us for a while...
Anyone I hope my post can help tracking this issue down...