I wanted a phone built for VoIP, not a smartphone that could run VoIP as one of many apps. This is it: a phone with the ability to connect to 802.11 networks and run SIP/RTP, which also works as a triband 2G handset.
I don't want lots of frills from a phone, and I don't have them here. It's got the usual phone book, SMS functionality, and so on. Ringtones are polyphonic only, not MP3. But the battery lasts a while, I can charge off any USB socket, and it connects happily to WPA and WPA2 networks, including MiFi-style 3G routers. (It can store four sets of 802.11 credentials, and will scan for open APs if those aren't available.)
The keypad is a bit fiddly, squeezed down to fit in the screen and with a four-way navigation ring with central key and two extra soft buttons compared with the Nokias I'm used to, but it only took a few minutes to get competent with it. The only ports are the headset and USB charging sockets, which have rubber covers; the unit ought to do reasonably well under light splashing.
Bought for £ 39+tax, SIM-free and unlocked, at http://www.sipgate.co.uk/voipshop/utstarcom/gf-210.