I have seen a general spoiler for the 813 episode.
Some folks don't like spoilers, so look away.
This gives us some very clear hints as to the direction they are going with this.
It's going to get very complicated.
Last warning.
Joey will be having a great deal of guilt over his new attraction to Rachel. In his confusion, he give Monica a muddled impression, and she goes and tells Phoebe that Joey is in love with her. In the meantime, Ross and Rachel agree not to learn the sex of their child - but Rachel peeks at the doctor's notes. Monica suggests that Chandler try a nice, relaxing bubble bath, but then can't get him out of the tub.
So we now have Phoebe running around thinking Joey is in love with her, Joey feeling like a dog because of Rachel, and Ross and Rachel acting like people who share a child.
So the writers perceive Joey with the mother of Ross' child as a moral dilemma, and important. And they've just made Phoebe vulnerable, when she didn't even need to be.
I think Joey's going to end up with Phoebe; otherwise, both Ross AND Phoebe will be hurt by a Joey/Rachel pairing, and I just don't think that's how they choose to end the show. This is going to be wrapped up very neatly and predictably.