Some Words About m0n0wall
m0n0wall is a project that is, according to its website (http://m0n0.ch/wall/), "aimed at creating a complete, embedded firewall software package that, when used together with an embedded PC, provides all the important features of commercial firewall boxes (including ease of use) at a fraction of the price (free software)."
m0n0wall is based on a stripped-down version of the FreeBSD operating system. It comes with a web server and PHP engine, as well as some other utilities.
m0n0wall can do a lot of things. In particular, I was only interested in its "captive portal" features. Just like publicip.net's offering, the captive portal can make sure that a customer who wants to use the hotspot will first provide a password using a simple web page (compare this to having to enter Wired Equivalent Privacy, or WEP, keys...think much easier). If users properly authenticate, then they can move on to surf using the hotspot's bandwidth. Without doing so, they would go nowhere.