A softphone is the general term used to describe a VoIP phone connection where software is installed on either a PC or smartphone and used instead of a normal telephone.
The PC or smartphone acts as the phone, but may have limited functionality in terms of more advanced features such as call transfer and call conferencing.
If you are planning on using an Android smartphone as a softphone, then many Android devices have a native SIP client built into the dialler that you can program with your extension settings. Using this method means that the extension is fully integrated with things like the native phonebook and missed call lists.
Mobile phone extensions are piggy-bank friendly – calls between these and your other extensions will be completely free. You can also set the mobile extension to ring at the same time as other phones, allowing you to answer office calls when you are away from your desk.
Softphones on a smart phone are designed to work through your data connection, so you will need to make sure that you have either a WiFi or 3G connection before you make or receive a call. And keep an eye on your data allowance! Calls made or received below a WiFi or 3G/4G data speed may suffer from jitter and low call quality.
If you are using a softphone on a PC then a headset with a microphone is required.