LG announced several new smartphones at the Mobile World Congress in February, and one of them has gone on sale already in South Korea. We don't know if the Optimus 4X HD will come to T-Mobile, but it could replace the Optimus 2X (renamed T-Mobile G2x). If it does, it could go head-to-head with the Samsung Galaxy S3 to be released later this year.

LG has promised to update the G2x to the Android 4.0 system eventually, but the Optimus 4X HD is running the system now. That could have implications for when the 4X HD launches if indeed it does come to the U.S. When LG announced the phone at MWC, it didn't tout it as a 4G LTE device; that, along with the naming convention had tech blog PC Mag's Sascha Segan predicting the eventual T-Mobile launch. There's no pricing or release info given yet.

Furthermore, because T-Mobile already has the Samsung Galaxy S2, it would make sense to see the S3 land there as well. That would give a boost to the T-Mobile lineup, whosr only addition this year so far has been the slightly overpriced Samsung Galaxy S Blaze 4G, coming March 28.

HTC's One S is coming to T-Mobile as well, but no release date or pricing has been announced yet. All three of the other major U.S. carriers are gearing up for big launches this summer, so the Optimus 4X HD could be part of T-Mobile's strategy as well. Start the slideshow to see how it stacks up against the powerful Samsung Galaxy S3.

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