 
  Google Voice is a great way to have a single number that people can  call and text if you have multiple devices. You can ever port your  number for $20. The service is free! This is how you can use it on your  FreedomPop phone.
1. Get a Google Voice number: Go to  voice.google.com . If you do not have a Google account, you can create  one. They will give you a number for free in the area that you choose. 
You must set up an existing phone number to forward to. You can use  your FreedomPop phone number. If you wish to use another number, you can  add it in the Settings (the gear icon) and the "Phones" tab. You may  add up to 7 phone numbers. Here you can also purchase the porting of  your number if you wish to use an existing cell phone number.
You can set your voice mail under the "Voicemail & Text" tab
2.  Install the Google Voice app: With this app you can text message and  check you voice mail. It will download this messages using whatever data  is available. When you open the app initially, it will ask for the  Google account. Select the account that you set the account up with. It  will then ask you to select a phone number for the phone; choose the  FreedomPop phone number. It will ask how you would like to dial. Select  "Do not use Google Voice to make any calls". This feature will NOT work  with FreedomPop. (For another phone with a different phone service, you  would select "Use Google Voice to make all calls" for it to show in the  Caller ID of the receiver.) We will get use a work around to get your  number to show up.
3. Install "Voice+ (Google Voice Callback)":  Search the Google Play store for "Google Voice Callback" and you will  find this program or click here: https://play.google.com/store/apps/details?id=hu.xilard.voiceplus  . Run the app and select the Google Account that is tied to Google  Voice. Then move the FreedomPop number up into the Visible numbers. For  default call type, use "Always Ask". I have found this setting to  constantly work. If you wish for it to dial immediately, select "Always  Google Voice". 
To use this app you must use the native dialer and not the FreedomPop  Messaging app to dial out. It will send the number you dialed through  the internet to Google Voice, it will call your FreedomPop phone, then  place the call. For it to properly work, you must open the Messaging  app. Click the menu key and select "Settings". Click on "Easy  configuration" and uncheck "Integrate with Android". Then click "Save"
Now do a test call with the native Phone app. Dial the number you wish  to call and press send. A box will pop up asking if which phone to call  you back on if you have it set to do so. Then it another box will  briefly show to cancel if it did not make the call in 5 seconds. You  will then receive a call with your Google Voice number as the Caller ID.  Answer it, and it will connect you to your number.
You may use  other apps to make and receive calls with Google Voice too like "Spare  Phone" and Groove IP. But these will not work after mid May 2014. I  personally think these are inferior solutions to the FreedomPop  Messaging app over 3G. Google Hangouts will eventually work for calling  out as well.
