T-Mobile does not recommend based on rated speed. The higher the class, the faster data can be consistently recorded, read, or transferred on the phone. For example if an SD card had a U rating of 1, the speed class would be 10 MB/s. This is usually a single digit and can be read as MB/s.

The class is printed on SD cards as an even number inside a C. Speed Class is a minimum speed based on a worst case scenario test.Rated Speed is maximum speed of the card and also what you would expect to approximately see in typical usage of writing or reading files on the card.SD card speed classes are different from speed ratings. Speed class: T-Mobile recommends SD cards with Class 6 or UHS Class 1 or higher.Size: This refers to the physical size of the card.Most smartphones can only take SD cards up to a certain size limit. A higher-capacity card increases the amount of data that can be stored.The storage or size of the SD card refers to how much memory the card has to store music, pictures, videos, apps, or other files.Memory size: Limits vary by smartphone, check the tech specs to determine what size is supported.Refer to the following classifications to assist in determing the SD card that will work best with your smartphone.

If you see these problems with an SD card inserted in a smartphone, upgrade to a faster SD card. Advanced features like HD video recording, transferring files, or apps that use the SD card, it is likely to cause freezing, crashes, slowness, or errors. Using an SD card without the proper speed class may work for basic storage. SD card memory size and speed ratings vary by OEM.

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