T-Mobile US provided a TSR of 4.0% over the last twelve months. Unfortunately this falls short of the market return. It's probably a good sign that the company has an even better long term track record, having provided shareholders with an annual TSR of 17% over five years. It's quite possible the business continues to execute with prowess, even as the share price gains are slowing. It's always interesting to track share price performance over the longer term. But to understand T-Mobile US better, we need to consider many other factors. For instance, we've identified 2 warning signs for T-Mobile US that you should be aware of.