UT Starcomm has released their F3000 clamshell style VoIP phone that SIP ready according to this news announcement.
Hopefully they have this working with hotspots that require log-in, but I tend to doubt that, so while you can log in at home and over a WEP’d or WPA’d network, the ability to use these while sipping a Latte’ at Starbucks, on between flights in an airport lounge, is likely still a ways off.