I spent couple of hours to find out that if you have already registered for the account before the service is launched, when you try to call someone, while using your cell, the box would appear as connecting and would not connect your cell phone.
Here are steps you need to do
1) Go to the google voice webpage (www.google.com/voice)
2) On the top right corner you will find settings tab, select this and from drop down select voice settings
3) In the first column of this page you will see your google voice number and an option to change to it
4) Select change it, you now have to agree to terms and conditions of google. It would also tell you that you can send free text messages from your account.
5) Change your number or select the previous one from the list.
6) You can even search for a good number by giving text like search for george and it will give you an option to find the number with the word george
7) Now call this number from your cell phone to confirm it TADA you are done
Let me know if it helps
