updated 04:23 pm EDT, Tue October 22, 2013
Plans scale up to 4.5GB for $40
T-Mobile is now available as default carrier on LTE models of the new iPad Air and iPad mini, according to Apple's website. In an unexpected move, the carrier is offering 200MB of monthly data for free; the next cheapest plan is Sprint's $15 tier, which includes 1GB. AT&T only offers 250MB for $15, and Verizon charges $20 for 1GB.
T-Mobile is also offering two paid tiers. $30 covers 2.5GB of data, while $40 pushes the limit to 4.5GB. For contrast, AT&T and Verizon are each offering 5GB for $50; Sprint is asking the same pricetag for 6GB.