No seriously, as far as I can tell, all that's being asked for this piece of mobile software is, "You see that vbaProject.bin file in the .xlsm file under the 'xl' directory? Yeah, ignore it's even there. Just don't touch it until the user hits save, then make sure that file, which hasn't been touched, is in the saved zip file."

* edited quote and to add:

Really --- if the phone version doesn't even support macros, there's no reason for it to touch the macro related files contained within the xlsm file. It kind of appears that someone had to do work in order to make it take a document with otherwise editable content and make it non editable because there's a file within the zip that provides extra functionality when used with a desktop client. Persisting unchanged files contained within a zip file to a newly saved copy of a zip file surely was thoroughly tested when "save" functionality was included I would hope .. at least to a point where Microsoft shouldn't be afraid of opening an Excel document write-enabled.