I've have the Zyxel 2000w v2, the Linksys WIP300 , the UtStarCom F3000 and the Hp iPaq 510.
I'm pretty sure all have be discontinued. the first 3 are dedicated SIP WiFi sets and have worked well with 3Cx from locations all over the world. One only does 802.11 b, one only g and one does both. The HP does not include STUN and is not meant to be used outside the local LAN that the PBX is running on, they tell you that in the documentation. It will register, but, most of the time will only give one way transmission.
I have has some issues with the sets maintaining registration if just left idle for a period of time, but because they are used primarily for outgoing calls it hasn't been a big issue. I'll have to shorten the registration time to see if that helps but many times the setting in the set itself are "overruled" by the PBX.
One of the big drawbacks is the lack of replacement batteries. There is no such thing as a standard generic phone battery so it may come down to having to rebuild one myself to keep these working in the future. All of the sets have advantages and disadvantages. One of the problems, that I've found when travelling is that without a browser built into the set you are out of luck using it at any "free" wifi hotspot that requires you to go through a "homepage" first.
