Here's my idea:
I think the whole island, and in fact, the whole TV show is really an elaborate illusion. All the characters are really physical manifestations of split personalities residing in the mind of one person. Something has occured and all the personalities have finally come together, having never "met" prior (so we think), and find themselves Lost on an island. Each of the characters has their own identity which you get a taste of as the show progresses. In the end there will probably be only one person left to save off the island, resulting in only one personality remaining.
The numbers respesent something important obviously. An idea is that the numbers/combination is the inmate number of the "real" person as he sits in prison somewhere waiting for his last few hours before death sentence.
Granted my ideas are exteme, but I'm taking a stab out in left field. I figure if this is all a mental fantasy taking place in someone's head, then that person must be under some kind of duress and stress in order for this to be happening NOW and not at some other time during in life.
Keep this in mind. The show operates as if a dream, where objects come and go at will. Things on the island, and events that take place there, don't quite follow a logical path. Many things just stand out as odd and out of place. A dream can operate much the same way. However I think this goes way beyond that of a dream, more like a mental confrontation with a myriad of mental elements all clashing and colliding together.