The Xperia Play has a native PS1 emulator to play Playstation 1 games. A couple of days ago a developer known as "yifanlu" released a tool that converted PSX ISOs to an apk for your Xperia Play. He decrypted the Crash Bandicoot PSX game that comes on all Play devices and created the tool. Not all PSX games work 100% and for games that don't work you should use the Android PSX Emulator known as FPse.
I think its awesome that something like this is finally done. Especially since I just got the Xperia Play a couple of weeks ago. :3 Here's the link to the tool.
http://forum.xda-developers.com/showthread.php?t=1201532
FF7 Works Great. Has some sound glitches.