[bernart]

Feedback and comments please. I am new at Asterisk. here is what I want to do.

I want to use Asterisk to:
- provide low cost VOIP service to a total of 10 users at 4 sites
- allowing traveling users access to low cost Voip service
- provide voice mail
- provide hunt for user [call 1st number, call 2nd number, voice mail]
- etc

Asterisk box resides at site #2 and have the following connections
- connected to a VOIP service providers with regular 10 digit number
- connected to other VOIP service providers
- connected to 3 other satellite sites via internet. all sites using dynamic IPs no known domains
- connected to SPA 3k with POTS line and Analog phone
- connected to 2 SIP phones
- behind router with NAT and firewall

Remote Site #1
- Internet connection
- Behind router with NAT and firewall
- SPA 3k with POTS line and Analog phone
Remote Sites 2-4
- Internet connection
- Behind router with NAT and Firewall
- SIP phones

Scenarios:
1. Traveling user in the vicinity of site #1 calls into site #1 SPA 3k POTS line wanting to connect to the Asterisk box in order to make call thru VOIP service provider
2. Traveling user in the vicinity of site #1 calls into site #1 SPA 3k POTS line wanting to connect to the Asterisk box in order to call another user at sites 2-4
3. Traveling user calls SPA 3K POTS line at the Asterisk box wanting to connect to remote site #1 and use their SPA 3K POTS line to make a call
4. Traveling user calls Asterisk via VOIP service provider 10 digit number wanting to make a call back call
5. Traveling user calls Asterisk via VOIP service provider 10 digit number wanting to use the VOIP service provider to place a call
6. Traveling user calls Asterisk via VOIP service provider 10 digit number wanting to place a call thru Remote site #1 SPA 3k POTS line
7. User at remote site 2-4 connects to Asterisk to call another user at remote site 2-4
8. User at remote site 2-4 connects to Asterisk to place a call thru remote site #1 SPA 3k POTS line
9. User at remote site 2-4 connects to Asterisk in order to place a call thru Voip service provider

My Problems/Concerns
- Any reasons why this should not work
- How does asterisk connect to remote sites
- How does VOIP line in/out of Asterisk work? How does it deal with multiple simultaneous in and out calls from the same service provider
- Firewall and NAT issues