Google voice : One Number :

Google Voice gives you one number for all of your phones — a phone number that is tied to you, not to a device or a location. Make and pick up calls, send and get texts, and read and listen to voicemails on your phone, tablet, or computer.

What you can do with Google Voice

• Text from your computer: Send text messages to up to five contacts at a time, straight from your computer's browser.
• Make voicemail as easy as email: Read transcriptions of your voicemails, add notes, download, and share voicemails.
• Customize your callers' experience: Screen calls and create personalized greetings for family, friends, or coworkers.
• Pick up calls from any phone: Choose to receive calls at home, work, or on your mobile phone, based on who's calling or when.
• Talk the way you want to: Make international and conference calls, block unwanted callers, and listen in on voicemails.

What you'll need to set up Google Voice

• Google Account
• Touch-tone phone, with a U.S. number
  • You'll select a type for each phone you add to Google Voice: Mobile, Work, or Home. (Text messages will only be sent to phones listed as Mobile.)
• Computer, with Internet access
  • Web browser: Google Chrome, Internet Explorer 8 and up, Firefox, Safari, Opera
  • Flash 8 and up: Visit Adobe's Flash Player page to confirm you've downloaded Flash and what your version is.
• Optional: Google Voice app on Android or iOS

Cost and availability of Google Voice

At this time, Google Voice is only available to U.S. Google Account users. Users with non-U.S. Google Accounts can make phone calls using Hangouts on a computer, Android device, or iOS device.

Almost all calls to the U.S. and Canada are free. A few U.S. and Canadian destinations will cost about USD 1 cent per minute, depending on the specific phone number and the local currency.

You can look up the cost through the calling credit page for your Google Account. You also can make calls to destinations outside of the U.S. and Canada with low international rates.

Get started with Google Voice

Choose an account option, then go to Google Voice and follow the prompts.

Via : https://support.google.com/voice/answer/115061?hl=en