asterisk

In a market full of choice and variety, it's funny that there are so few good SIP/VoIP phones around.
There are cheap toy phones being sold at premium prices .
There are expensive professional phones which just don't work properly.

Then there's this: Cisco bought Linksys who bought Sipura. This unholy combination looks something like: quality hardware + cheap prices + quality software.

The Linksys SPA942 really is a Cisco phone with Sipura software at Linksys prices (about £60 exVAT currently). It works with Asterisk, first time and every time. No reboots, no crashes, no voodoo required to get it to talk to the server over IP-NAT. Good weighted handset, clear sound, easy to use interface (and big, bright screen to view the interface on). Even the number buttons have that perfect weighting and clicky feel. No rubber buttons here. The web interface is a beauty to behold; it can be as simple to use as putting in the extension number and password, but there are options to change everything if you need to - and it's fairly logical and easy on the eyes.

Recently I've deployed three Asterisk based VoIP servers. I've used Trixbox ISOs, as I had good experiences using Asterisk@Home a few years ago.

In general, things have gone well. Here's a few things I've come across:

Asterisk in VMWare is far from ideal. I've had a lot of problems with quality and the start of audio being clipped off. This perhaps is as much due to my massively overloaded server as anything else.

Trixbox 2.2 (the current release) is based on CentOS 4.5, which is RHEL4 and runs Linux kernel 2.6.9. The hardware support is far from up to date - if you have something like a newer cheap SATA controller you'll probably lack support - while it'll claim Linux compatibility due to drivers being in the latest kernels. As a side note, modern cheap IDE and SATA controllers tend to be rubbish anyway. Never use onboard software RAID, the bugs and issues I've seen are great and varied.

VoIP phones are immature. They really are. You have the high end Cisco which is solid and performs brilliantly with Cisco servers, yet is virtually useless with the SIP standard due to bugs and generally piss-poor implementation. Then you have the cheaper phones which will actually work (hooray!) but be of such low quality that you wonder why you'd bother. And there are things like what might be nice features included in the firmware which simply don't work (case in point: Snom/Elmeg IP290. Pops up a VMail link when there's voicemail, but tried to open the wrong SIP URL, and is NOT configurable in the web interface with the rest of the config options - I later find an Asterisk-side workaround which gets this working).