After a few days of work, I now have a pre-alpha version of Devicescape‘s hotspot login agent running on our iPhone. It is not ready for release, but it is doing basic logins, and has a simple UI (though mostly a status screen at the moment).
The screenshot shows a connection to a FON AP, but I have also logged in to our in-house test hotspot, the T-Mobile one in Starbucks across the road and a German T-Mobile hotspot we have in our shielded room for testing against.
Still more to do on this (at the very least a button for logging out of the network would be useful), but it is a start.
None of this would have been possible without the progress made by the folks at the Phone Dev Wiki of course, especially on the toolchain.
Thanks also to Eric Sadun for the screenshot utility.