1) I live in the UK
2) I have broadband via BT
3) I have a WiFi router and Modem
4) I want to be able to make cheap VOIP calls via a wifi handset
Questions
1) Which is the best provider in terms of quality and reliability and
secondly price
2) I want to use a WiFi handset rather than a headset. Which is the
best WiFi handset

Vonage is the answer.  I live in Jamaica and use Vonage, and recently
spent 10 days in the UK.  I brought my Vonage modem with me and it
worked perfectly on my parents' BT broadband (DSL) connection.  I
wired my Vonage modem through their Netgear wireless router.

Vonage has very cheap packages (US$15/month for 500 minutes).  While
they do not offer local UK service at this point, they do offer London
(020) numbers.  Calls within the UK cost about US$0.03 per minute.

You can use a regular, wired handset with Vonage through their modem
or, beginning this Spring/Summer 2005, you can use their new WiFi
handset:
http://www.vonage.com/corporate/press_ces.php?PR=2005_01_04_6
http://investorrelations.utstar.com/ReleaseDetail.cfm?ReleaseID=151788