Feature at Macworld on the best choices for iPhone-Fi: I wrote this feature for Macworld as a rundown of the best ways to find (and possibly pay for) Wi-Fi for an iPhone. Because the iPhone has a full-fledged browser, you'll be able to connect to locations that have gateway pages for terms of service acceptance, login, or payment. This includes Boingo, it turns out.
Yesterday, the firm wrote me to correct a misunderstanding. While Boingo uses a software client to allow automatic logins to their aggregated network's partner locations, the software client isn't a strict requirement. Most of Boingo's partners also have gateway pages that allow you to select a roaming partner, including all their airport locations (Boingo operates a number of airports themselves through an acquisition). This is great, because the very best U.S. and worldwide subscription deals are through Boingo, and iPhone users can tap into that.
The iPhone's features include VPN support--a helpful reader corrected me on that yesterday--and that's going to be problematic for most VPN users. Why? Because many corporations have moved to SSL-based VPNs, and Apple's Mac OS X includes only IPsec over L2TP and PPTP. I'm not sure if there's a generic way to support SSL-based VPNs without being able to edit the configuration file or install a specific one. Update: The iPhone supports just IPsec and PPTP.
Most of the hotspot-VPN services use specially configured SSL-based clients, too. HotSpotVPN is the only firm I know offering PPTP-based subscription VPN access (their legacy service, as they moved their main offering to SSL); post others you know in the comments below.