If you're not a fan of Google+, then the ability to call people with your Google Voice number via the Hangouts app was probably not something you cared about. However, Google has now added calling privileges to the Web version of Google Voice. This means that users don't need a Google+ account, just their original Google email log-in, to place calls.
Step 1: Log in to Google Voice on the Web.
Step 2: In the call or text box on the left, enter the number, and then choose Hangouts from the Phone to call with drop-down menu.
Step 3: After you click Connect, a new Hangouts window will appear. Press the Call button and you'll be connected to the number you provided.
Google seems to be moving slower than a snail's pace when it comes to updating the Voice service. However, this new ability to make calls without a Google+ account demonstrates that Google is still working on it. Should any future change limit your access to saved texts and voice mail, you can also check out this post on how to back up your Google Voice data.