I think you need to make players feel comfortable talking first. Here is a drill I use to try and encourage players to talk. I hope I can explain it.

Divide your players into 2/3 teams with even numbers on each team. Get each team to stand in a line (one behind the other about arms length apart). The first player on each team has a ball. The idea is for each team to get the ball to the end of their line, rather than just passing it any way they choose the first player needs to turn to the right and pass on the ball the next player to his left - so on and so on until it gets to the last player who then must run to the front of the line and start the process again. The game ends when the player who was at the front of the line is back at the front.  

I normally allow the player to do this the first time with no instruction from me other than the rules. Nearly always some player will turn the wrong way and make a mess of it. Then I step in and say to the players wouldn't it be much easier to help your team by shouting which way the player needs to turn. You will then get all your teams shouting left/right heloing the player and using their voice.

Next you can change instead of turning left/right - you do over/under (First player goes over his head, second player goes under his legs and repeat as above).

When they have mastered both of those and to introduce more complexity you can combine both (Left - right - over - under - left - right - over - under)

Might not be everybodys idea of a good drill but from experience I have found it a great way to get players using their voice and breaking the silence.

Rob Carroll
www.thevideoanalyst.com

I found this helped. Split your team up into groups 5 or 6 with a ball. Get them to stand in close, shoulder to shoulder, hands out ready to catch the ball. When the ball is passed/popped to a player they all must say the players name. You will need to encourage them at first and keep reminding them to pass the ball quickly.

When they are doing this well, get two groups to going together.  This also works wonders if you have new team members.  Everyone learns names fast.