So do we know when OB ends? Or does it just crossover to full game?

We don't know for sure yet.

most mmo's last ob's do continue over to real game possibly, hopefully, etc.

dunno about that, every big open beta i know of for mmos purged all characters at end of the beta.

World of Warcraft(never played this but i know they nuked at end of open beta)
Champions Online
Aion
City of heroes(same as WAR)
ect...

most any big mmo wipe at end of open beta, why? because its considered an unfair advantage, just because you were in open beta you got this massive jump on everyone else. Now fact dbo is a free mmo may come into play but i wont hold my breath. I fully expect all characters to be wiped at end of open beta its only practical to do. Add to the fact is some zenny exploit being done, could have some toons with millions of zenny have it do to a bug in beta! just my feelings on whole deal i went into beta expecting a wipe at end.

Hopefully CJ Internet 2009 Q4 or 2010 Q1 presentations will show when Full Service will begin... They'll probably do a crossover from OBT to FS (although I'm not really sure how Netmarble does it with their other mmorpg's between OBT and Full Service.)

open beta wont end at 04.02.2010 ?

There's no reason to assume that. We were promised some 95% of the game's full content in pieces. We haven't gotten any of those pieces yet.