The S4 accepts SD and MMC cards. SD cards max out at 2Gb. The 4Gb and 8Gb cards are actually SDHC (Secure Digital High Capacity) cards, not SD cards, and thus will not work in devices designed for SD cards. Compatibility goes only one way--SD cards will work in SDHC devices but not the other way around.
Answers & Comments
The S4 accepts SD and MMC cards. SD cards max out at 2Gb. The 4Gb and 8Gb cards are actually SDHC (Secure Digital High Capacity) cards, not SD cards, and thus will not work in devices designed for SD cards. Compatibility goes only one way--SD cards will work in SDHC devices but not the other way around.