I can take calls when wifi is enabled....I dont have a data package so I have it turned off with nodata...
I had those same problems with the call hanging. As soon as a hit answer it would send them to voicemail...I recooked a rom last week that I took out the programs I dont use leaving alot of extra memory left. I havent had a problem with it since. Could also be the dialer now that I think about it.
I installed the mobile vista dialer into the rom with an oem I made from the cab and no problems...(knock on wood)..I used to install a cab for the dialer.
heres the dialer if interested.
http://forum.ppcgeeks.com/showthread.php?t=18086