If you don't know what's a softphone then your are missing something very important

A softphone is a program for making telephone calls over the Internet via the Voip (voice over ip) internet protocol, using a computer rather than dedicated hardware. The softphone can be installed on a piece of equipment such as a desktop, mobile device, or a laptop and allows the user to place and receive calls without requiring an actual telephone set. a softphone is designed to behave like a traditional telephone, with all the features an actual telephone or mobile phone. and often additional features such as user presence indication and video

Why use a softfone?

• Annonimity: no more eavsdroping since a softfone is just a software based phone, so you can be sure that no third party is listening to your calls and messages
• Take Your Business Phone Wherever You Go : If you are an employee who work from home or frequently travel to clients or vendors. you will be able to take your business phones with you. From a client's office, hotel room, or even a coffee shop, you can simply boot up your laptops and have your phone ready to go. Using the softphone, you can answer incoming calls as well as make outgoing calls, just as if you were sitting at your desk using a physical phone.
• Keep Personal Cell Numbers Private
• Make Video Calls and host Video Conferences
• and many more

Popular and best softfones:

Zoiper

Stop eavesdropping on your calls, encrypt your VoIP calls!
Don't like it when people eavesdrop on your conversations? Neither do we, that's why we offer free encryption for all your text, voice and video communications with TLS/SRTP and ZRTP.
Zoiper comes with free, military grade end to end encryption for voice and video. (if your server or service provider supports it).
Zoiper supports these standardized encryption methods:

• TLS
• SRTP
• ZRTP (mobile and zoiper desktop beta)

linphone

linphone is a free open source VoIP SIP client for smartphones, tablets and desktop platforms. available for all platforms, Android,iOS, Windows and Linux. and offers many features:
- HD audio and video calls
- Integration with iOS/Android push notifications systems
- Audio conferences and advanced calling features
- Instant messaging (IM), group chat and file sharing
- Account creation and remote configuration (via QR code or URL)
- Secure communications with end-to-end encryption
- Fully SIP-based, for all calling, presence and IM features

groundwire

By Acrobits, they offer two business apps for Android and iOS: Groundwire and Acrobits Softphone, Acrobits Softphone and Groundwire utilize push notification that let you Be notified of incoming and missed calls, voicemails, and texts.