I have installed the Advertising Management modification for phpBB 3.0 countless times. It’s very popular to serve ads, obviously and to have easy ways to place them within phpBB. There was a development extension for phpBB 3.1 that I was able to get working for some clients.
Now an extension for phpBB 3.2 is available but even better it’s being supported as an official extension of the phpBB group. So from now on it should always be available. It has a slightly different name but was obviously built on top of the old modification. It’s now called the Advertisement Management extension.
See the announcement and video here.