Voip handset in UK

Hi

I am looking for a cheap VOIP phone / handset (not usb) in the UK for my daughter at university. I want her to be able to call us on our ATA in Portugal free by calling our IP number.

I am not sure about protocols but it would have to be compatible with our ATA she will be calling. Also, the handset will have to cope with NAT as she is connected to the internet via a D-Link internet gateway.

Thanks