Google Voice is not yet open for users outside the US, but are planning to expand our service to additional countries in the future.
However if you are in the US you can now port you existing mobile number to google:
What is BT Ribbit ?
The Ribbit Platform is a reliable, scalable and future-proof multi-protocol, open platform that supports rich voice innovation and integration. The foundation of our platform is the Ribbit SmartSwitch™, a revolutionary multi-protocol carrier-grade, Lucent certified, CLASS 5 softswitch. It is the Ribbit SmartSwitch that allows calls to be initiated and answered on multiple devices and run across multiple communication protocols, networks, and device types.
Google have launched a Voice and Video VOIP chat add-on extension plug-in for Firefox on OS-X and WXP & WVS !
http://www.ic-talk.co.uk/21cn/Default.asp & http://www.switchedonuk.org/
BT, in consultation with the UK telecommunications industry, and with input from Ofcom, is upgrading its phone, broadband and ISDN lines to a next-generation network. This evolution in communications will not only provide the services all of us enjoy today, but will also enable more people to access exciting new services in the future.
There will be some disruption to your phone, broadband and ISDN services in the months and weeks leading up to the work and on the nights when your services get switched-on. This will typically mean that you will be unable to make outbound calls for up to three minutes or receive incoming calls for up to 30 minutes when phone services are switched-on. If you have a broadband service, this will be interrupted for up to 10 minutes when broadband services are switched-on.
http://www.tilgin.com/ supply voice, video & data gateways and set top box multi-media centers