I've found a real useful SIP setup primer for you

As you may know, Internet 2 is a consortium of 207 universities, as well as private and public sectorparticipants dedeicated to, as they put it,creating "aleading edge network capability for the national research community," and "enablerevolutionary Internet applications. Internet2's SIP.

As you may know, Internet 2 is a consortium of 207 universities, as well as private and public sectorparticipants dedeicated to, as they put it,creating "aleading edge network capability for the national research community," and "enablerevolutionary Internet applications.

Internet2's SIP.edu program is dedicated to enabling university users to receive VoIP calls at their university email address. More than 140,000 users are enabled, and the number is climbing steadily.

When you have that much experience implementing SIP (Session Initiation Protocol) solutions, stands to reason that any how-to advice you choose to impart will reflect real-world problems and solutions, not just lab benchmarking.

Even if you are not at an educational institution, that's why I recommend that you read the SIP.edu Cookbook. While not extremely technical, this amply-illustrated series of Web pages (not PDFs) offers sections on how to get started, on DNS configuration, proxy utilization,gateway deployment, directory mapping issues, security considerations, and the pros and cons of hard phones vs. soft phones.