For most people, Asterisk is not easy to use. Several companies are offering setups that are very easy to use. See http://www.coneenterprises.com/phone_solutions.ph
p and http://fonality.com/ for and interesting solution based on Asterisk. The interface rivals Vonage which is great for VoIP. The next generation of the software will allow database calls based on caller id so you can launch outlook or another database and pull up information based on the caller id. This system can add users and extentions easily. You can even setup a very complex call center queue.