Micro SD cards up to 2Gb will work in all Micro SD compatible devices, cards above 4Gb are compliant with a new standard called MicroSD High capacity or Micro SDHC for short. MicroSDHC cards will only work in devices showing the following logos, adapters are required for standard and mini size card slots. Card readers also need to have the correct logo to work with the cards. High capacity cards are not backward compatible with standard Micro SD devices.
Standard and high speed Premier Micro SD cards are available, the Premier cards can read and write data faster than the standard cards, although this can also depend on the device. High capacity cards and devices comply with the following speed class ratings wich specify a minimum sustained write speed for SDHC/miniSDHC/microSDHC cards (Class 2: 2 MB/s; Class 4: 4 MB/s; Class 6: 6 MB/s). look for the following logos to identify your card speed.