Well a lot of quistions here but no answers.
To give you all a general idea I will put in some answers.
If you want to no more just send me a email and I will try to help you all out.
You have to start at the basics, what is IP telephony and what is Voice over IP. Second thing you need to know is what kind of network do i need to get started in the firts place. Protocols is not that important, only if you know what your goals are with IP Telephony. SIp or H323 or G723.
It all depence on featers your customer needs in his company.
And than you need to find out which vendor is the best choice to work with.
Take a look at the Cisco E-learning site. There a lot of free of charge cources avalable which will help you to understand IP Telephony. Or take a look at Amazon.com they have some pretty goods books on Voip and IP Telephony. Or try to contact a local Cisco Sales office.
Specialy if you need material for educational use, Cisco is verry supportive on this.
Or sen me a email and perhapse I can help you. Take a look at my company site, specialy on the trainings site.
Morgan de Ruiter