OnePlus is the fourth most popular smartphone brand at T-Mobile and has become the fifth most popular US smartphone brand for devices over $500 overall, according to reports from two analyst firms.

The cult smartphone maker previously sold its phones exclusively online in the US, but broke out into stores when it agreed to sell its OnePlus 6T phone through T-Mobile in October. While Apple and Samsung still dominate US smartphone sales, OnePlus is coming up.

"At T-Mobile, with roughly two months of sale in Q4 2018, OnePlus captured 2.43 percent share ... the fourth largest brand at T-Mobile in Q4 2018. At this run rate, OnePlus could become the third largest at T-Mobile," surpassing LG, said Neil Shah of Counterpoint Research, which tracks mobile phone sales by carrier.

OnePlus is doing even better with online sales than in stores. "For online sales at T-Mobile, OnePlus did well; [it] captured 6.3 percent share and was the third largest brand with two months of sale in Q4 2018," Shah said.

In the overall market for flagship phones, OnePlus is now fifth after Apple, Samsung, Google, and LG, according to research firm IDC's Mobile Phone Tracker.

IDC says the market for phones over $500 in the US is "heavily controlled by Apple and Samsung." Several different analysis firms have told me over the past year that the high-end market here is around 90 percent Apple and Samsung, leaving the other players fighting for the leftover 10 percent.

Most of the non-Apple/Samsung sales in the US go on at the low end of the market, making OnePlus an overall ninth in the US market, according to IDC. The actual overall top five manufacturers are Apple, Samsung, LG, Alcatel, and Motorola, the firm tells me. Alcatel does not sell any expensive phones in the US and most of Motorola's sales are of its low-priced G models.

It's Still a Huge Milestone

It's a huge milestone for OnePlus to make it into the top five of any slice of the US market. Carrier distribution helps, but that doesn't guarantee anything. The history of AT&T is littered with discarded partnerships and exclusives where AT&T promised to sell HTC, Nokia, Microsoft, ZTE, or Asus phones, made them disappear after a few weeks, and went back to selling iPhones.

T-Mobile, on the other hand, seems to be still committed to OnePlus. I stopped into T-Mobile's flagship Times Square store on Sunday. The store was eerily empty overall, but the OnePlus 6T was still front and center, prominently displayed—three months after it launched.

It's surprisingly rare to see a carrier prominently displaying a non Apple or Samsung phone months after it has launched @oneplus @TMobile pic.twitter.com/cD7FWndfS6 — OG Evolution (@saschasegan) February 10, 2019

Google is running a similar playbook, it seems. The online giant stands at No. 3 in IDC's tracker for phones over $500, probably thanks to its marketing deal with Verizon, where Verizon continues to push the phone.

OnePlus said in December that its first-month sales globally were up by 249 percent over its previous model—meaning at least 2.5 million OnePlus 6Ts were sold in the first month. But it didn't break that number out by country.

While Americans tend to criticize carrier sales exclusives, it's clear that in this case, OnePlus' T-Mobile partnership is working.