[Serusers] Managing different Area Codes in a centralized SER

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