Can a micro-SDHC memory card and a micro-SDXC memory card be used interchangeably?

Not the same, but has the same fit and size. Micro-SDXC has a different file system and can have much larger capacity but may NOT BE compatible with older phones (micro-SDHC equipped) because the storage file system is different. The micro-SDXC is much faster in handling data.

Go to the scandisk web site and on the right hand side of the page it allows you to enter the manufacture, (camera, cellphone, etc.,) and it will return what cards are compatible with the product you want to use.

http://www.sandisk.com/products/memory-cards/microsd/

@Wealthadvisor Thank you very much for that very helpful link.

Not always; it’ll fit, but the addressing scheme is different, and possibly newer than the device you’re installing the card in.