Every major IP PBX vendor builds a proprietary softphone that is customized to tap into its back-end system like no other standards-based Session Initiation Protocol endpoint can.

The use of these proprietary methods both stymies the interoperability between vendors and limits the number of third-party companies that will develop softphone applications for a given vendor's system. Therefore, it's legitimate to ask what you gain by going proprietary. We took a look at the two softphones Alcatel-Lucent offers with its OmniPCX Enterprise IP PBX to help quantify the proprietary advantage.

Overall, the major advantage of vendor-specific softphones is their ability to access the full feature set of the underlying PBX. Standards-based softphones are limited to features defined within the protocol and not the underlying VOIP system. A second advantage is ease of use; the softphone functions the same as the vendor's hard phone so the user learning curve is nearly eliminated.

Alcatel-Lucent's My IP Touch (we examined Version 1.0.0.3) is a graphical representation of the company's IP Touch 4068 hard phone that can be installed on any Microsoft Windows computer. The application requires less than 50MB of hard disk space and works with the minimum standard PC specification on the market today. The softphone, like a hard phone, is licensed as an individual device.

Once installed, the user registers with the OmniPCX Enterprise and is given an extension and the permitted telephony features. To place a call, the user clicks on the handset on the screen and selects the numbers. The buttons on the display portion of the softphone change according to the call state. So, for example, if a user were to go off hook and place a call, once connected, a previously blank button would display the transfer option. The user could click on transfer and enter the desired number.

Volume controls, message waiting indicator light and the full qwerty-based keyboard layout also are shown in the display. The keyboard represented on the computer screen lets users perform directory lookups and send messages to another user's phone while either party is on another call.

All of the OmniPCX Enterprise's more than 500 call features, such as account code charging, call park and call pickup, are available to softphone users. There is a second skin -- a different representation of My IP Touch softphone -- that takes up a smaller footprint on the user's desktop while still providing full functionality.

As with any softphone, performance is heavily determined by the underlying PC platform. Our test system comprised a Pentium M processor running Microsoft Windows XP SP2, 1GB of RAM, and integrated microphone and sound card. A headset is recommended for optimal sound quality and performance, but even with the built-in microphone and speakers on the test laptop, sound quality was acceptable and latency was less than 100 msec.