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Just in time for the holidays, Apple has started selling the iPhone 5 unlocked and free of carrier subsidies or subscription requirements. The price tag for this stocking stuffer prohibits it from impulse buy status, though. The 16GB model costs $649, and prices only go up from there.

Before you plunk down your cash for a subscription-free Siri, however, you'll want to read the fine print about which cellular networks the unlocked iPhone works with. The unlocked iPhone 5 only works with supported GSM networks, which means it won't work on the CDMA-based Verizon or Sprint networks. It will, however, function just fine on AT&T's service -- or T-Mobile's.

T-Mobile doesn't offer the iPhone 5, but it runs a GSM network and the company just so happens to offer handy-dandy nano-SIM cards for people who have unlocked iPhone 5s.  In fact, the company is doing all it can to woo unlocked iPhone 5 owners to its service, currently offering said nano-SIM cards absolutely free when you sign up for a two year plan and even waiving the usual $35 activation fee. Unless you're picking up an iPhone simply to use it on the T-Mobile network, however, signing up for a two year contract somewhat takes away from the allure of an unlocked handset.

The company's "Unlimited Nationwide 4G Data Plan" reaches across the country, while AT&T offers individual and shared data plans that relies on tiered payment levels and overage charges. AT&T, however, offers true 4G LTE in some locations, while T-Mobile's 4G technology is of the HSPA+ variety.

Speaking of LTE, Engadget points out that Apple doesn't disclose which LTE bands the unlocked iPhone 5 works with, so you shouldn't count on LTE access outside the United States until Apple clarifies the situation.

Head over to the Apple website if you're interested if picking up an unlocked iPhone 5.