Getting a 4G iPad Air? Here's how to outsmart the carriers

　　The iPad Air and new Retina-display iPad Mini are among the hottest gadgets this holiday season, and of course many people will want to get the cellular-enabled versions so they can browse without looking for Wi-Fi. Here's how you can get the most for your money — or no money at all.
　　First, we have to look at the elephant in the room: T-Mobile's absolutely free plan, which gets you 200 MB of high-speed data for life. If you really want to save money, this is really the only option — it even makes that extra $130 for the cellular iPad seem reasonable. For that matter, there's no need to even buy a new iPad — you can bring in any compatible tablet and T-Mobile will activate it gratis.
　　If, however, you want to do more than check email, download some books and apps and browse Wikipedia, you'll need more that 200 MB of data, and for that you must pay.
　　Getting cellular data with your iPad can be done in two ways: add the iPad to your existing plan, or sign up for an iPad-specific one.
　　If you're already paying for unlimited data for your smartphone, it might be best to take door number one and pay whatever it costs to let your iPad share that connection. On AT&T, T-Mobile and Verizon, it'll cost you $10 to add a tablet to your plan; at Sprint, you'll have to pay $15 for a tablet plan, but it adds 2 GB to your limit (and their unlimited plans are cheaper to begin with).
　　But if you'd like to be able to switch the cellular data on your iPad on and off month by month, you'll want to get one of the special iPad plans. The goal of these plans is maximum mobility and a decent amount of data; if 200 MB isn't enough, 1 gig probably isn't, either. But who wants to pay an extra $50 a month?
　　The $30-a-month plans offer the most basic and flexible value, then, and of those we recommend AT&T's for the following reasons:
　　You're not bound by contracts, so you can jump on and off at will (unlike AT&T's ordinary tablet plans)
　　Verizon offers less data for $30, and on top of that their and Sprint's network hardware isn't as compatible internationally
　　AT&T generally has better coverage than Sprint or T-Mobile
　　But wait. Here's the best part. After you activate with AT&T, stop by T-Mobile and start an account with them, too! T-Mobile told NBC News before that an AT&T iPad (and many other phones and tablets) should work fine on their network and vice versa. We haven't tested it out (yet), but there's no technical reason it shouldn't work like a charm. And the price is right.
　　That way, you can subsist on the free plan during months when you just need to check email on the train — but can reactivate your $30 AT&T plan quickly and easily should you want to stream music during a day at the park. All you need to to is pop open the SIM slot (you may need a paper clip) and swap cards. The rest should take care of itself, since there's no hardware difference between T-Mobile and AT&T iPads.
　　The same advice should apply to the new iPad Mini whenever it comes out, and also for other iPads and tablets that support both AT&T and T-Mobile.