Why did T-Mobile US's operating expenses decline in Q3 2024?

T-Mobile US's operating expenses declined in Q3 2024 due to a combination of factors:

1. **Decrease in Total Devices Sold**: Lower upgrades to postpaid and prepaid plans, along with a reduction in the total number of devices sold, particularly in the prepaid and assurance wireless segments, contributed to the decline in operating expenses. This strategic shift likely led to cost savings in device-related expenses.
2. **Cost Management**: The company has emphasized strong cost management across the enterprise, which has resulted in increased operating income, net income, and Adjusted OIBDA. This proactive approach to cost management has likely played a role in the overall decrease in operating expenses.

In summary, T-Mobile US's operating expenses declined in Q3 2024 due to a combination of decreased costs related to device sales and strategic cost management initiatives.