I think I know what AT&T is up to with the recent data plan change: they’re trying to switch everyone to a pay-per-MB plan just before videoconferencing hits the mobile market big time.

I, perhaps like you, only use about 100 MB a month because I only use my iPhone for information. Email, a website or two per day, and maps. I use my iPhone a lot, but I don’t think of myself as a multimedia user. So when the new rate plan came out, my first thought was, “Excellent! I can save $15 per month with no change in my behavior!”

And that’s the trick: Within the next year, the behavior of iPhone users is about to change, and ATT wants to get us to willingly opt-in to a pay-per-MB plan before we realize that. Because once videoconferencing hits the iPhone, even email-only iPhone users will be gobbling up huge data charges if they choose to see their phone conversations in addition to hearing them.

And then we’ll all wish we had stayed with the all-you-can-use plan.