It's very possible for it to be Baldy's (so rude of me not to know his name). Not a lot of women show at 2 months. A lot of them really don't know their pregnant until 2 or 3 months. Now that's not every women, but some. And also unless you've been planning for it and know from the moment of conception. They've been on the island for about 2 1/2 months. It is very possible she got a quickie from the guy before she left. Seems so unlike sweet Sun to do that, but we don't really know her all that well. She surely surprised me when she told him she was glad she couldn't have a baby. You'd think, by her sweet nature, she'd want one. I'm glad now that she's happy about it though. I would like to think it's Jin's however. And the messed up part is that they need a DNA test to know if it is his, if he ever has doubts. Dharma could probably provide that for them.
If the unknown magical properties of the island can make Locke walk, then they most certainly can turn at least one of Jin's sperm into a good healthy swimmer. I wasn't that blown away by this miracle after a seeing a paralyzed man walk
i'm saying it's Jin. As much as they started to imply that she and baldy may have something "more" between them, I don't think she slept with him. We know she still went to the airport the day she was supposed to run from Jin, so Mr. Baldy couldn't have been too important to her. Plus at the very end of the episode, when Jin left her in the garden as she asked, she touched her belly and the smile she had on her face just looked so genuine and happy. I really do think it is Jin's and it is all a "miracle"
I think it is the other guy. They have been on the island for what 40 days or a little more? There was a look in her eyes after Jin adn her hugged, that said she was relieved in a way, and didn't seem like she was all upfront about everything.
Anyway, it could be Jin's too, as I agree with everybody else that Island had a part of it is his.
I want to say Jin, and that the island had something to do with it.
Also, I'd like to say that if Sun had gotten pregnant by "Baldy" before she took off, there chances are high that she could have lost the baby from the trauma of the plane crash, as well as Charlie's assault.
I'm going with Baldy for two reasons: the look on Sun's face after Jin believes her about him being the only one; and the fact that they only "made up" and started relations again after the Tailies and Fusies reunited - which could not have been more than 8-10 days ago - not enough time to get a clearly positive preganancy test.