[Help] Information needed for right download

Hi,

Anyone that has some information on what is the best download for my needs please let me know. The idea is: (for about 50-80 phones)

Trunk line is rented from the telco & connects to asterix.
asterix is programmed with an extension # for each rep for inbound.
800# connects to the trunk line.
Each extension connects to a SIP phone on the desk of the REP.
The Trunk Line & Asterix server need to be in the US or Canada

Is it possible to route the outbound calls over a VOIP gateway?

Every piece of information will be appreciated.

Jessy