Yesterday AT&T announced it would no longer offer unlimited data plans for its iPhone and iPad customers. (Seemed to me like kind of a "bait and switch" to alter the iPad data plan only a month into the product's life, though those of us who already signed up for unlimited 3G data can keep this plan.)
For the iPhone, "DataPlus" will cost $15 for a maximum data download of 200 megabytes a month while "DataPro" will be $25 for a maximum download of 2 gigabytes a month.
This means I have a couple of decisions to make. I looked up the data usage on my iPhone in recent months to see where my monthly consumption pattern falls:

It's usually over 200MB per month. But what is most interesting is the drop-off in the last few weeks, a period not represented on this chart; with only four days left in the current billing cycle, I have only used 128 megabytes of data. The obvious reason for this is the arrival of my iPad. Assuming a large chunk of my data consumption has shifted to the iPad, I ought to be able to save $15 a month from by going with the "DataPlus" plan on the iPhone.
And for the time being, I think I will keep the unlimited data plan for the iPad; I'm not sure I will need it after the summer because of the ubiquity of WiFi on campus, but until I figure out how I will be deploying the iPad when I travel, I don't want to lose the unlimited data plan option, especially since I've gotten accustomed to streaming movies on Netflix on the device. Moreover, the arrival of multitasking a few months from now may see me using Pandora a lot more than I do now. I can always downgrade the data plan in the future.