How is it done (wifi connection pages)

[sdfgeoff]

At a couple of places around town there are free wifi access points that are just plain unencrypted (open security type if you like).
But when you first connect to them, they take you to some webpage with terms and conditions and a connect button (or if they're mean, a password box).

'Scuse be for being noobish here, but how is this done? I'm guessing it requires special software on the router doing so?



I'll lay out what I'm looking for a way to do, just in case you have some other ideas.
I have an old android smartphone, flashed to android 4.0.1 (or something like that), that needs a new purpose in life. I want to set it up as a standalone server. An open wifi network with a single webpage. Getting a server on android is no problem, there are apps for that. Setting up a network is no problem, wifi tethering is built in, but a person connecting does not want to try pinging every IP address.... When they connect, how can they be redirected to the page it hosts?

[BUBBALOU]

You mean something like this

http://www.howtoforge.com/wifi_hotspot_setup

[sdfgeoff]

Fairly similar except using an android phone, not charging people for it (seeing as it doesn't connect to the internet), and I'd preferably code my own.

For my own reference, here are two links.