After Linksys bought Sipura (Linksys itself is now owned by Cisco) they re branded the next generation of Sipura products, the SPA9XX series, as Linksys products.  This series improves upon the original 841 in terms of features (Power over Ethernet on some models and a built in switch on some models are the main improvements) as well as build quality, the phones now feel like a high quality product.

The Linksys SPA921 is the cheapest of the Linksys SPA9XX series but offers the same quality as other models in the series, just not all of the same features.  For instance the SPA922 is similar to the 921 but includes Power over Ethernet (which means if you do not already have PoE compatible equipment you must purchase either a PoE injector or a power cube for the phone) as well as a built in 10/100 Ethernet switch so that if you only have a single Ethernet drop to a desk you can plug that into the phone and the computer into the phone, versus having to purchase a separate switch and plugging both the phone and the computer into the switch and the switch into the single drop.  

 

The one nice feature for a home office that the SPA922 does have that the SPA921 does not is a back light for the LCD.  If you want a back lit phone for home use you could purchase the SPA922 but keep in mind the additional cost of having to purchase a power cube or a PoE injector.  I find it very odd that Linksys would provide a back light on a PoE phone but not on a phone that plugs directly into the wall for electricity, usually it is the other way around.

All of the SPA series of products only work with Session Initiation Protocol (SIP).  SIP is of course the dominant protocol out there for both IP phones and servers but also for Internet Telephone Service Providers (ITSPs).  Personally I like to have my SIP devices all connect to Asterisk and then have Asterisk make IAX2 protocol connections out to my ITSP since not only does IAX2 support encryption (who knows how good it is, it was thrown in a few versions back but rarely used by anyone) but I also don't have to have as many ports open on my firewall.

 

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