Cellular carriers inhabit a Twilight Zone universe. For example, they offer "unlimited" data plans that are, in fact, limited and subject to "reasonable use," meaning whatever they choose it to mean at the particular moment. And they often charge very different prices per megabyte of data, based on the device you happen to be using -- an odd result of their move to consumption-based billing, which was ostensibly meant to implement fair costs for all users, rather than let data hogs get a nearly free ride at everyone else's expense.
Dubious differences within carrier plans
The curious pricing scheme that is emerging leads to the following oddities with carriers' plans.
AT&T charges smartphone users 8 cents per megabyte for 200MB of data, but 3G USB modem and MiFi users pay 18 cents per megabyte for the same 200MB. Corporate smartpone users pay 2 cents per megabyte ($45 per 2GB), but USB and MiFi users fork over just 1 cent per megabyte ($60 for 5GB). And AT&T charges pay-as-you-go tablet users $15 per each additional 200MB of usage, but it charges pay-as-you-go smartphone users $10.24 per additional 1MB -- that's 128 times the price per megabyte.
T-Mobile charges smartphone users less per megabyte than it does tablet and USB/MiFi users. You pay 5 cents per megabyte for the basic smartphone data plan ($10 per 200MB) but 10 cents if you use one of the other devices ($25 for 250MB). It makes sense that the company's unlimited data plans' pricing favors smartphone users ($30 versus $40), as tablets and laptops are likely to eat up more data than smartphones. But when you're paying for a set amount of data, the 2:1 cost difference doesn't make sense.
Verizon Wireless charges twice as much per megabyte for additional data than it does for the original data: A smartphone user pays 1 cent per megabyte ($20 for 2GB) for the first 2GB, but 2 cents per megabyte ($20 for 2GB) for the next 2GB. Sprint has a greater disconnect in its 3GB pricing: 1 cent per megabyte in its initial tablet and USB/MiFi plans ($30 for 2GB and $60 for 5GB), but 5 cents per additional megabyte. Sprint charges netbook users less for additional megabytes (5 cents) than for the initial megabytes (8 cents, based on $40 for 50MB). However, that makes sense since the netbook is sold at a subsidized price, so the initial $40 includes a payback amount for the device's subsidy.