You can have this feature without doing the upgrade, here is how I did it;

1.) Do the first three steps listed in the above post,then do these steps.
2.) Click on the icon (3 people) that's under the world icon on the desktop and select 'New Internet call'
3.) from the menu select 'Tools' then 'Accounts'.
4.) In 'Accounts' select 'New' an Account setup wizard will pop up.
5.) Select 'sip' from the drop down menu.
6.) In 'User name' put the ten digit gizmo phone number and after '@' put prox01.sipphone.com, then your gizmo password in the password space.
7.) At bottom of page select 'Advanced', then 'Authentication' there you will again enter your 10 digit gizmo phone and password.

To receive calls and text messages make sure you have 'Presence' set to On or Away. You will see the 'Presence' icon in the upper Status bar.