I feel a little disloyal, given that VoIP is also a feature of Messenger, but I've opted for Skype for cutting the cost of my international calls now I'm here in the US (I shudder to think what my next mobile phone bill will look like). I've set up a UK SkypeIn number (contact me directly if you'd like it) so that folks from the UK can call us without incurring high costs themselves.
But having to leave my computer on all the time (or loiter around next to it) is a pain. So today's toy du jour is Netgear's Skype Wifi Phone. It connects to my home wireless network (or any other wireless network that doesn't need browser-based authentication, which does limit its portability a little) and lets me call Skype and non-Skype contacts (via SkypeOut).
I haven't had a chance to test the phone in anger yet, but the set-up process was very simple, making it easy for me to select the wireless network, enter the WEP key, and then enter my Skype username and password. Only slightly annoying thing is that the recharging cable plugs into a rather fiddly mini-USB socket on the bottom of the phone. A desktop charger (per most normal wireless phones) would have been nice. And it's not that cheap - $225 on Amazon (though they're doing a $30 rebate at the moment).
The Netgear's main competitor is a new Skype Wifi phone from Belkin. The Belkin's a little cheaper, but seems a little less bedded down, and is a bit more shoddily built, according to a comparison of the two devices on Gizmodo.
Will post again with more feedback.