Yeah, I checked the PSP resolution and is adding borders as you told me, and is something like this:
AddBorders(0,36,0,36) [the movie is 2.4 and because of that I have 36 instead of 34]
But iPhone have a smaller display and I like more this:
AddBorders(0,0,0,72)
In my examples I used SSA subtitles, because SRT can not contain info about font and position.
enjoy,
Mtz