Pure Java VoIP Telephony Servers?

Curt Cox asks: "My company develops pure Java web applications, using Win32 and Linux, that are then deployed on Linux servers. One bell/whistle that many customers want is telephony integration. Our current solution is to handle calls through a dedicated Windows NT/TAPI box with an expensive telephony card. The thing I like least about this solution is that adding phone lines is such a pain. I would really like to use the net2phone or dialpad networks and avoid physical lines completely. Unfortunately, their client software is written to interface with speakers and microphones, and not programs. Are there any pure Java solutions for VoIP telephony?"