Your customer will be able to transfer calls across the tie lines, call each other, page over each others paging system and call out over each others local lines.
For example......
Someone at site A in California will be able to pick up their handset, dial an access code (or put it on a single button), get dial tone of the other side (side B in New York) dial any extension number and have it ring the phone.
They will be able to pick up, press the E&M pool button, dial New York's outside line pool access code and get local dial tone in New York.
They will also be able to press the pool button and make a page over New York's paging speakers.
In addition, if a call comes to California and it actually needs to go to someone in New York, they can press transfer, press the pool button, dial the appropriate extension, have the person pick up, announce the call and hang up to complete the transfer.
It works vise versa from Site B New York to Site A in California.
Is this what you were looking for?
MRoberts