Well, if you really want that, you can play World Championship Poker 3 (though the load times on PSP really aren't good). It allows for the PSP and PS2 versions to play on the same lobby. WCP2 did this as well.
Yup, I already tried WCP2 on PSP, it was somewhat nice online, but I didn't like the "bluff system". I'm really looking forward to Stacked. I never tried it on PS2 or Xbox, but it seems to be the most complete Texas Hold 'Em game.