I see this question all the time... Cat 10 or Cat 4 mictoSD card.
The answer is, the T899 LTE Ativ S is Cat 10 certified, the i8750 GSM Ativ S is Cat 4 certified. So on a GSM Ativ S using a Cat 10 may or may not work. So get a Cat4 32GB for the i8750. In fact the Cat10 is only faster for large read write operations, for random read writes a Cat4 is faster. There are two different Ativ S phones, different chipset.
The answer is, the T899 LTE Ativ S is Cat 10 certified, the i8750 GSM Ativ S is Cat 4 certified. So on a GSM Ativ S using a Cat 10 may or may not work. So get a Cat4 32GB for the i8750. In fact the Cat10 is only faster for large read write operations, for random read writes a Cat4 is faster. There are two different Ativ S phones, different chipset.