I know in global mode it allows both systems to operate but they aren't really both active. If the phone is using the CDMA system it will not receive calls or texts from the GSM side.
Here is a video of how the Acer DX900 running WinMO6.1 handles the two lines. I'd like to see our TP2 be able to do the same...
http://www.youtube.com/watch?v=igGjoHe8fPI