Hey,
I just got a message from T-mobile of the following contents:
Free Msg from T-Mobile: By 3/8/08 go to
Unsupported Browser from your pc to get software for your Pearl 8100 (includeds a Daylight Savings patch)
I ussually get these type of messages a bit after a new update, however I got one already for 4.2.1.107 not long after it came out. It's interesting that it says "by 3/8/08" as I don't remember these messages saying dates before. I don't know if it necessarily means anything, but hopefully this means that 4.3 should soon be available (or 4.5?). There isn't anything new on the bbupgrade page yet.
Feel free to correct me if my assumptions are entirely off base.