Didn't work for me. I have a ps3slim 250gb and used an original MGS4 disc. This could be a problem in the game itself coz I read forums addressing similar issues dating back to 2008-09 when there was no jailbreaking PS3s.
Anyways, I tried using the original disc, then backed it up to hdd, tried the above method, nothing worked so I just skipped that part using a save I got from the net. It skips the part where the PS1 stage is emulated. Doesn't skip much except a very small cutscene where snake wakes up from a dream.
I would recommend using a save to skip that part.