Recently a friend of mine has just got a new Macbook Pro 13" after her old macbook was stolen from a shop. She dropped it round for me to do the initial set-up for her, configure her mail client, install/upgrade apps etc.
She has a USB ZTE Dongle from ThreeUK, she was worried that the dongle would not work with Mountain Lion, as she was told from a certain retailer. It does still work, just not with the drivers that are pre-installed on the dongle. If you do need the latest drivers then you can get them from the ThreeUK Support page.
Following that link will show you the drivers for Windows (XP, Vista and Windows 7) and MacOS (Tiger 10.4, Leopard 10.5, Snow Leopard 10.6, Lion 10.7, Mountain Lion 10.8), as well as Firmware for certain models.
I am always interested in your thoughts so if you have any comments or feedback then please feel free to add any comments, or you can mail me here.