I havent used *now, but as i understand it *now comes with asterisk so you don’t need to install asterisk again.
That depends. If you can connect to your PBX via any sort of VoIP protocol, ie SIP, IAX2, h323, etc then Asterisk can use it to send out your calls over Ethernet.
If not then you will need some kind of card to connect to your PBX. If your pbx only has analog channels you will need a Digium TDM400 series card or equivalent. Sangoma is good, stay away from the TDM400 clones. If it has a free PRI (T1/E1/J1) type port then you need a Digium PRI card (make sure it’s for the right PCI slot type). Sangoma also makes good PRI cards.
So short version, Asterisk can do VoIP out of the box but as soon as you get off of VoIP/ethernet you need hardware
and damn, it looks like bacon beat me to it