[Asterisk-Users] transferring 3000 SIP calls

[Vic]

Hi, all,

we are building a forwarding station in Japan where we
would be receiving and forwarding over 3000 SIP calls at
the same time.

The calls will be offered to us via a carrier as SIP and
we will forward the call via the same carrier as SIP.

The callflow would look like this:

1. SIP call come in
2. System will authenticate the call based on the number
3. Check the billing information and if it is ok, forward
the call to another number (as SIP)
4. If call is not ok, system will connect the call to IVR
for an announcement and touch-tone input

We are thinking about using Asterisk for this. 
How big of a system should it be?

Can we use one linux box for this (and another for backup)
or will it be something humangously huge?

Thanks,
Vic