Advanced IP Scanner or Angry IP Scanner will do that for you. You can also look in your ARP cache on the local server. Use the command arp -A on the server and it will report back the IP address assigned to MAC addresses and whether they are dynamic or static. Combining voice and video calls in a user-friendly interface, CounterPath's X-Lite helps you seamlessly transition from a traditional phone environment into the world of Voice over IP. Download CounterPath Corporation is a leading provider of innovative desktop and mobile VoIP software products and solutions.
OK, let’s get started its free, quick and easy Also Read: VOIP App Download for Windows There are many free apps that can be found by searching for ‘sip softphone’ in google or the apple/android stores, we recommend the following free ones: Notes: Transcom VOIP works over both WiFi and GSM, however, for GSM you need to have a good 3G connection and if possible, use the G729 codec as it uses less bandwidth, which makes it suitable for 3G. Most softphone applications have the G729 codec, but normally at an additional upgrade cost of around £4.99.
Transcom VOIP users are entitled to a 50% discount on Transco ISP services, contact us for a voucher code. VOIP for MAC & VOIP for PC Express talk for MAC. 
Voip A Lot For Macbook
Express Talk Product: Express Talk Company: NCH Software OS: Windows, MacOS Overview: Express Talk works like a telephone to let you make calls through your computer. Name anybody by way of the web who additionally has a softphone put in and in the event, you enroll with a VoIP gateway service firm you name common phone numbers as effectively. With Express Talk, you could potentially call someone using their internet IP (eg. Ar9285 mac os x.
“bob@1.2.3.4”) but this is not usually practical. It is much easier to use a friendly address like “bob@myphoneco.com”. 
To have this you need to sign up for a SIP proxy server.
Voipalot
This is almost always free to signup for and usually requires nothing more than an email address. See our Recommended SIP Service Providers List for a list of options. Read: Some of the companies also provide gateway services. This means connecting phone calls to ordinary (non-internet or analog PSTN) phone lines.