You don want try and run hard-phones on SSL/VPN connection, because the
whole idea of SSL/VPN is to enable mobile users to get central office
connectivity through any web browser.
Juniper has successfully tested used IPSoftphone using our SSL/VPN
technology. I use it on a regular basis both in the road-warrior mode
(both signaling and RTP are over the IP connection), as well as in the
telecommuter mode (where only control signaling is over the IP
connection and voice traffic is over the PSTN network), and it works
very well.