How to use with Vonage?

If I am trying to use Asterisk tie together 5-10 different phone lines, some Vonage some POTS, in geographically different locations. How do I do that?

The objective is for customers to call one number for our company, get an auto-attendant to enter an employee’s name (push 1 for Joe, 2 for Mike), and get to that virtual employee.

Do I have to sign up for a new virtual IP phone number that uses SIP to reach my Asterisk server, and that server contacts the 5-10 different virtual employees?

Can anyone please explain?

Setup a teliax or broadvoice account and use that as the main number. Then tie the extensions to vonage phone numbers, something like:

exten => s,1,Answer
exten => s,2,Wait(1)
exten => s,3,DigitTimeout,2
exten => s,4,ResponseTimeout,20
exten => s,5,Background(maingreeting)

exten => 1,1,Dial(SIP/8675309)
exten => 2,1,Dial(SIP/2564286000)
exten => 3,1,Dial(SIP/3037574611)