Hi Choi,
Thank you for taking the time to share your experience. We're glad to hear AT&T worked well for you, and we appreciate your feedback regarding the T-Mobile coverage. Coverage can vary depending on the location, and we continuously work to improve the experience for our customers. Our service supports multiple network providers, so in many areas you can manually switch to another available network if one isn't providing a reliable connection.
If you experience this again or need any assistance, please don't hesitate to reach out to our support team. We're always happy to help.