Prosecutors tried to prove Tuesday that Steven Avery lured Teresa Halbach to his family's auto salvage yard on the day he allegedly killed her.
Cellular company workers Bobbi Dohrwardt and Laura Schadrie testified at Avery's trial in Chilton.
They said Avery's cell phone made three calls to Halbach's cell, and he twice used the Star-67 feature that hid his identity.
Prosecutors said Avery called Auto Trader Magazine to have Halbach take pictures of a vehicle his sister wanted to sell.
The calls indicated Halbach was alive at 2:30 p.m. on Oct. 31, 2005.
The final call was made a couple hours later, and it was not clear if it was answered or got sent to voicemail.
Meanwhile, the defense was barred from asking Schadrie if somebody heard Halbach's voice messages for three days, starting the day she was said to have been killed.
Attorney Jerome Buting said the messages were evidence of police bias in the investigation and they showed the possibility Halbach could still have been alive.
Prosecutor Ken Kratz said the issue was not relevant. Judge Patrick Willis says it can be explored later if need be.