A 'softphone' is a piece of software which can be downloaded and installed onto your computer, which allows you to experience VoIP technology and experiment with setup and call quality.
You will also need a headset and microphone - the Plantronics 400 is a great example. Alternatively you could use the speakers and microphone built into your laptop.
You can download Telephone from the official project website at http://code.google.com/p/telephone/. When you have downloaded the software, you must configure it before you can make or receive phone calls. This is a straightforward process and is described briefly below.
After installation and starting the program, it will display the following window.
Type your name, or the display name you would like to use, into the Full Name field. This is used when calling other SIP phones - you could display your name here or your company name, or your telephone number.
Enter your seven-digit Gradwell extension number in the User Name field, and your extension password in the Password field.
In the Domain field, enter the registration server specified in the welcome email you have received. This is usually sip.gradwell.net.
Click Done. The main Telephone window will appear.
You will need to configure the NAT proxy in order to properly make and receive calls through our network. In the menu bar at the top of the screen, click Telephone, and then click Preferences. In the Preferences window, click on the Network tab. Configure it so that it looks like the following - note that Local SIP Port has been left empty.
Close this window using the red close button in the top-left corner. When prompted, click Save.
Type a telephone number into the field here and press the Return key on the keyboard to dial that number.
Telephone also interacts with the built-in Mac address book; if you have a contact in the address book with a telephone number, type their name and the field will auto-complete.
You may need to configure your headset or other audio devices - for example, you may want to choose an external microphone. To change these, go to Preferences. Click on the Sound tab. You may choose devices to use for incoming audio, outgoing audio, and the ringer, and which sound to play when ringing.
To edit or add/remove accounts - for example, to change your extension password - go to Preferences, then click Accounts. Click on an account to modify it, or click the + and - icons to add or remove extensions.