This just hit the app store and will probably be pulled by Apple due to their app store policies (eg http://reviews.cnet.com/8301-19512_7-10277725-233.html)
The bargain is not only the free app but the thousands of roms you can play for free by using this app!
iPhone: http://itunes.apple.com/au/app/imame/id485639079?mt=8
bsdll's guide (thanks!):
Search for and download a file called "mame37b7_roms.zip". You'll have to do that bit for yourself, don't worry it's easy to find.
Copy the zip file somewhere, and call it "rom.zip". Also extract the file into seperate folder (which will give you tons of zip files).
Install some program to view your phone. iExplorer, i-FunBox are two free well known programs. Personally I use i-FunBox.
Navigate to "User Applications -> iMame -> Documents". Copy all of the zip files into there.
Navigate to "User Applications -> iMame -> iMAME.app". Copy the rom.zip file into there.
Open iMame on the phone. Press Option, then Options, scroll to the bottom and tap Rescan All ROMS.
Enjoy.
Thanks for posting the utube vid I'll give it a shot in the morning. Now to find ghosts and ghouls.