“There is a known issue with some hotspots where the iPhone 3.0′s captive
network support is forcing a browser to open and when the user closes
the browser to open iPassConnect, the iPhone OS releases the IP address
and disassociates the user from the hotspot. This means that when the
user opens iPassConnect, there is no network to login to…because the
user is no longer associated. Apple has produced a fix in the OS 3.1
beta update. We have not been informed of an official release date but
expect it to come sometime in September. If you have any further
questions, feel free to give us a call toll-free 24×7 at 866-849-2853
(in the U.S./Canada), or internationally at 979-361-1636.”

Shame it doesn’t work but (a) it’s a known problem, (b) a fix is in the works, and (c) they responded almost immediately to my email. Good customer service.