[Serusers] Managing different Area Codes in a centralized SER

[Freddy - VoiceFinder Peru SA]

Hello 
I have this scenario:

We are an ITSP trying to use a centralized SER to provide Telephony
services in several cities, each city has assigned the same number
range for clients that is 85XXXX (X ~ 0 to 9) including its area code,
usually when users call to another in the same city dont need to dial
area code before called number unless they makes a "long distance"
call, for example: when user 851234 from NY calls to 851234 in FL must
dial 305-851234.

I think, and please correct me if I am wrong, that the most reliable
way to manage those users in different area codes in one server is
using Ser´s multiple domain feature so I have this:

Domain 1: NY.sipdomain.com
Domain 1 assigned numbers: 85XXXX
Domain 1 Prefix: 631

Domain 2: FL.sipdomain.com
Domain 2 assigned numbers: 85XXXX
Domain 2 Prefix: 305

Domain 3: CA.sipdomain.com ,  etc....

I dont want to register users using areacode+number (too long) and I
could not register two users with same number in different domain, so

1.- How to configure Multiple Domain support in Ser?
2.- How can I configure ser to allow Interdomain calls?
3.- Caller-id or ANI for local calls (same domain) dont have to
include its area code unless they makes a "long distance" call (to
allow callback feature and because normal phones can´t include domain
in its screen) as a normal pstn system works.
 
please someone guide me on this issues.

thanks

Freddy