It's extremely hard for new smartphone brands to establish partnerships with U.S. carriers —including AT&T, Verizon, Sprint and T-Mobile.
It's why Lenovo acquired Motorola Mobility from Google in 2014. In that deal, Lenovo specifically called out Motorola's "great carrier partnerships" and "strong presence in the U.S." as two reasons for the acquisition.
Other phone makers such as One Plus, Huawei and Blu have turned to outlets such as Amazon to sell smartphones. Even new devices from well-known people in the space, such as the Essential phone from the father of Android, Andy Rubin, was only picked up by Sprint.
"The U.S. market for handsets is strongly controlled by the carriers," Richardson said. "To obtain distribution with carriers it's necessary to get carrier approval through a stringent and costly testing process. Xiaomi will need to invest in this. If it chooses to only go after the open market, its market opportunity would be severely curtailed. If successful in getting through carrier-testing and then getting ranged, it will have to master the art of supporting the carriers' way of going to market. This is very different than the process Xiaomi has used so far, although it is adapting quite quickly to varying market conditions as it expands internationally."
Moorhead thinks Xiaomi might be able to pull off those relationships, however. "Given Xiaomi uses Qualcomm chipsets and doesn't sell carrier equipment, I'm not foreseeing as large of issues with carriers," he said.