Can anyone identify this Korean drama from before 2008?

There was this drama (I believe it is a Korean drama, but it may also
be Chinese or Japanese) that aired in China in July/August 2008. I
don't remember what channel it was, but it had a fairly late timeslot
at around 10 or 11pm. It was dubbed in Mandarin (unless it's a Chinese
drama, but I don't think it is).

What I remember is that there are two guys and two girls. One of the
girls is poor, but she tries to pretend she's wealthier, I think,
until one day one of the guys sees her father selling stuff in a
subway. I think one or both girls are flight attendants or something
related to the airport. Both guys like the poor girl, I believe, but
one of them has a relationship with her that involves a ring that
holds some sort of importance. At one point (later on in the series,
perhaps?) there is a scene with the girl and one of the guys at a
beach. One of the guys also punches the other one.

Sorry this jumps around so much, but I hope it sounds familiar to
someone!