A couple of weeks ago, OnePlus announced its second smartphone of the year, the low-cost OnePlus X. The OnePlus X is an impressive little phone: it has a bright, sharp display, premium design, and clean software. And it has an aggressively low price of just $250. It doesn't have a dream spec sheet — the processor is woefully dated — but for the price, the OnePlus X seems pretty hard to beat.

But it has one major flaw that keeps me from recommending this phone to anyone living in the US. It's an unlocked phone, which OnePlus advertises as compatible with LTE networks on both AT&T and T-Mobile. However, the OnePlus X lacks support for AT&T's most widely used LTE frequency. Further, it doesn't have support for a frequency that T-Mobile is rapidly transitioning its network to. (It almost goes without saying, but the OnePlus X doesn't work at all with Verizon and Sprint's networks, and it is not advertised as being capable of doing so.)

If you use the OnePlus X on AT&T, expect HSPA data

That means that while the OnePlus X is capable of connecting to AT&T's LTE network, it can't in many areas because it can't talk to the 700MHz frequency (also known as LTE Band 17) AT&T most often uses. In my experience, using the OnePlus X on AT&T in New York City and surrounding areas for the past week, I was unable to keep an LTE signal for more than just a couple of minutes. Most of the time the OnePlus X was stuck on AT&T's HSPA network, which is much slower in both uploads and downloads than LTE. All of these issues also apply to the MVNOs that use AT&T's LTE network, such as StraightTalk or Tracfone.

Depending on where you live, you might have better luck using the OnePlus X on T-Mobile, at least for the time being. But T-Mobile is aggressively moving its network over to the 700MHz spectrum it owns the rights to (Band 12), and there are certain areas of the country that rely mostly on it already. If you have a OnePlus X in those areas, the best connection you'll get is HSPA.

OnePlus confirmed to me that the X is not compatible with AT&T's Band 17 or T-Mobile's Band 12, and it says there are no plans to add support for them in the future, via a hardware tweak or software update. It's not clear to me why this decision was made, but omitting support for the most popular LTE frequency on the largest carrier the phone can work on boggles the mind. Three long years ago, Google's Nexus 4 launched without LTE, which was disappointing, but forgivable for the time. But in 2015, it's not.

Lack of proper LTE support is inexcusable in 2015

Every other unlocked phone sold in the US that I've used this year has much better support for AT&T's LTE network, and many of them even include support for T-Mobile's Band 12. Phones such as Motorola's Moto G and Alcatel OneTouch's Idol 3, both which sell for $179, can access AT&T's full LTE network. (You'll have to pay a little more to get proper T-Mobile Band 12 support, at least for now.) If you're in the market for a low-cost, unlocked smartphone in the US, either of those would be a much smarter purchase than the OnePlus X.

Of course, this only applies to if you're living in the US. If you're in Canada or Europe, the OnePlus X should get an LTE signal on most carriers. That makes it an attractive smartphone at a really great price, provided you can navigate OnePlus' arcane invite system and actually purchase one.

But for those of us in the US, the OnePlus X's lack of proper LTE support makes it an easy skip. There are too many other excellent options available at equally attractive prices to make it worth wasting your time with the OnePlus X.

Verge Video: OnePlus X hands-on