Our interoperability tests featured Pingtel's SIPxchange SIP server, which we thought would be a good reference for SIP implementation because Pingtel has been in the business for some time and recently made its SIP server an open-source product (you can download it at www.sipfoundry.org). In addition, we used Pingtel's Xpressa SIP phone in our test bed. In general, we found that the phones we tested can handle features like hold, transfer and conferencing without any difficulties, even in a mixed, multivendor environment. However, message-waiting notifications posed some problems. We left voicemail messages for all the phones, and we couldn't get the MWI (message waiting indicator) to light on the ipDialog and Zultys phones. We worked with ipDialog, Zultys and Pingtel but were unable to solve the problem.
These less expensive phones have smaller screens and fewer feature buttons. And though they don't support a wide range of codecs, they do support both the G.711 and G.729 codecs for toll-quality audio. Most of the higher-priced phones we tested last year had full-duplex speakerphones, but only ipDialog offers a full-duplex speakerphone at this low price.
All three phones have as much as or more functionality than you'd find on a low-end business phone. For example, the Snom 200 and the ipDialog SipTone II Ethernet Phone both have LCD screens for Caller ID. On legacy phone systems, this feature typically is found only on more expensive digital sets. However, the phones we tested lack some features you'd expect on an enterprise IP phone. For example, Zultys' ZIP 2 doesn't support the IEEE 802.3af PoE (Power over Ethernet) standard--you must plug the phone into a power outlet, and you can't manage the phone's battery backup from the wiring closet. Still, the ZIP 2 is priced at less than $100.
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