These two phone models look almost the same. But the Linksys SPA942 has been discontinued while the Cisco SPA504G looks like an improved Linksys SPA942. Both phones offer easy configuration via a web interface, both have excellent sound quality. Both have a good feel to them with a large LCD display.
The Cisco SPA504G offers HD quality sound via the G.722 wideband audio codec and is a 4 line phone. It also a better speakerphone as compared to the SPA942.
For most users however, the differences will not matter much. The audio quality is great even without HD and most people do not require 4 lines on a phone.
On the Cisco SPA504G, when two phones with HD engage in a phone session, you should see a smalled “HD” icon show up.
The Linksys SPA942 is available on Ebay in “like new” condition for $30 – $40. The SPA504G costs a bit more and you could score a used phone from anywhere between $50 – $90.
If your work location is not wired for “Power Over Ethernet” (POE) then you should look for used phones that are sold with a power adapter. A new power adapter should cost about $10 or thereabouts but a lot of the used phones come with a power adapter.
Also make sure that the phones are “unlocked” before bidding on an IP phone. While unlocked phones can be reset, its often not easy. When handing out phones to sales agents, remote workers etc., these phones are the way to go. The performance is terrific and the price makes the phones close to disposable.
There is another phone from a company called “Grandstream” which offers a pretty good HD capable IP phone – The GXP 1400 (No POE) and the GXP 1405 (Integrated POE). You can get this phone for under $50 brand new and shipped. I just do not care for its smaller display but for all practical purposes this is a full-featured IP phone.
For a new organization, IP phones are the cost cutting way to go. All your need are some phone and a business VoIP server provider.