The maximum size of supported SD card depends on the operating system NOT on the hardware. Please see the below list.
Brand
OS
Max. SD size
M3 RED
Windows CE 4.2
2 GB
M3 GREEN
Windows CE 5.0
4 GB
M3 T, M3 POS
Windows CE 5.0
32 GB
M3 SMART CE
Windows CE 6.0
32 GB
M3 SKY
Windows Mobile 5.0
2 GB
M3 SKY, MM3
Windows Mobile 6.1
32 GB
M3 ORANGE, M3 SMART WM
Windows Mobile 6.5
32 GB
M3 ORP/ORS
Windows Embedded Handheld 6.5(WM)
32 GB
M3 ORC
Windows Embedded Handheld 6.0(CE)
32 GB
M3 BLACK
Windows Embedded Handheld 6.5(WM)
32 GB
The recommended SD card brands are SanDISK and Transcend. Other Cards are likely to work. However, these need to be tested to ensure they meet user requirements.
Note that since the SD memory size is limited by the OS, it will only support 2GB or less when updating OS using SD card (Only M3 Smart, ORP, ORS and ORC can use up to 32GB for OS update). Also, M3 RED does not support OS update via SD.