Looks like there is an update for the AceKard 2i that allows it to be used on DSi systems running firmware 1.4. (the official 1.4 update from Nintendo disabled all flash cartridges).
The complete update instructions are over at Xpertron; download the 1.4 firmware update, drop the appropriate .nds file onto the MicroSD card, boot into the AceKard 2i menu and run the firmware updater.
If you have updated your DSi to 1.4 firmware already, you will need to beg/borrow/steal a DSi with an older firmware or a DS Lite to perform the update.
It is also a good idea to upgrade to the latest AceKard 2i menu software…
I did the update using a DS Lite and it appears to work ok- but the AceKard 2i now appears as ‘Danny Phantom Urban Jungle THQ’ to the DSi….