GP32emu had a massive WIP news about ZXAdvance. Be sure to check it out. A few lines from the post at GP32emu:

The HiVE sent me the first beta of his port of ZXAdvance (Spectrum emulator) originally for the GBA to the GP32. HiVE is spending this month working on the emulator and has so far got a ‘barebones’ version up and running. At the moment there is no sound in the emulator but real ULA emulation has been added and everything is still extremely fast and is expected to stay this way (no speed throttling has been added yet). If you are familiar with the GBA version you will know its very nicely presented with a great menu system, HiVE told me that he is creating something very nice for the GP32 version, but he wont tell me exactly what yet 😉

http://www.gp32emu.com/