I recently got a nice hint from one of our members that the Iphone version of Memory Maps uses the QCT format for the maps.
Standard maps in this format are unencrypted, only "valuable" content like topo and nautical maps are secured and have the ending QC3.
The QCT files can be converted with several programs and by using a Python script that is available on the net, however the current version of Global Mapper can handle the files as well.
This give us the use of the following formats in OZI:
OZF, OZF2, OZFX, OZFX3 - the well known Ozi formats
PNG - with the corresponding .map file
ECW - again with the corresponding map file even if the ECW contains calibration data. You have to import the ECW to create a .map file
QC3 - usable for the Android version of Ozi, not tested on other versions yet

Since the Iphone versions of Memory Maps are available for a large range of countries it might be worth checking if you need up to date maps for the use in Ozi.
Programs of choice for all converting needs: Ozi PC, Global Mapper, Adobe (needs plugins).
Programs of choice for OZI-only maps: old versions of the IMG2OZF and MAPMERGE tool. The new versions create encrypted maps that can only be used in OZI.
If you use the older versions of the tool all programs compatible with OZI maps can use them.