The difference between TMUSP and TMUS is that the "with P" ticker is for a TMobile Preferred Stock offering. The "without P" ticker is for TMobile common stock. The difference between the apparent percentage yields is due to Yahoo! Stock misreporting the dividend on the preferred stock for the common stock, which has not paid a dividend (thanks Brick for pointing this out!)
Preferred stock holders get paid first in the event of liquidation, in most scenarios they get paid first. They sometimes get better returns. They typically lack voting rights, and after a grace period, they may be recalled by the company at a fixed price (set when they were issued).
Common stock holders can vote to alter the board of directors, and are the epitome of the typical "I own a trivial fraction of the company" model that most people think of when owning stocks.
As the common stock is valued at much less, it appears that the percent yield is much higher, but in reality, it's 0%.