Many universities are now setting up to broadcast lectures over their LANs, often in video. Many students simply watch from their rooms, or even watch later. There are many downsides to this (fewer show up in class) but the movement is growing.
Here’s a simple addition that would be a bonanza for the cell companies. Arrange to offer broadcast of lectures to student cell phones. In this case, I mean live, and primarily for those who are running late to class. They could call into the number, put on their bluetooth headset and hear the start of the lecture on the way in. All the lecture hall has to do is put the audio into a phone that calls a conference bridge (standard stuff all the companies have already) and then students can call into the bridge to hear the lecture. In fact, the cell company should probably pay the school for all the minutes they would bill.
This need not apply only to lectures at universities. All sorts of talks and large meetings could do the same, including sessions at conferences.
Perhaps it would encourage tardyness, but you could also make the latecomers wait outside (listening) for an appropriate pause at which to enter.