Asterisk application

Dear Friends,

in the last meeting I was able to attend I had a crash (too much!) for 
Asterisk.

I'm not interested in using it as a PBX for "normal" phone lines. VoIP 
is the thing attracting me mostly.

The scenario is:

two offices, one in italy and one in China. every workstation in Italy 
has a Softphone and an Extension number, the same for each workstation 
in the chinese office.

At this point is it possible to call from a workstation in China a 
workstation in Italy just dialing with the soft phone the extension 
number? I'm not interested in making phone calls to external phone 
numbers, just a way to let colleagues of the two offices talk at no 
cost.

How many asterisk servers do I need, one for each office or only one?

Thanks

Matteo.

P.S.

I'm in Italy now, I will stay here until the spring festival but i 
continue to follow the discussion on the list