While mobile virtual network operators may appear to be back in fashion, none of them are significant players among US wireless carriers. The largest of what are commonly—but incorrectly—called MVNOs, including Boost and Metro in the US, have long since ceased to be MVNOs, or never were. These are, instead, flanker brands for the major mobile network operators that own and operate them, including Sprint and T-Mobile, respectively, for the abovementioned.
