asterisk users - Jul 2007 - Asterisk with 2 Public IP-Is it possible?

Good morning,

we actually have 2 Asterisks 1.2 running on one server each of them in a 
XEN Dom and connected together with a IAX trunk. This setup allow us to 
use our both public IP (different ISP's) and to have failover solution 
in case of a problem on one of the ISP's line.

Is it a way in 1.4 to do the same but with only one Asterisk instance?

First problem we see is that externalip in sip.conf can be fixed for 
only one IP. Second is, if we could put 2 external IP's, if one packet 
is going out with, let's say PublicIP#1, and at this time the link from 
this ISP is down, packets will -helped by external routing- go out 
through the second line but never come back.

Does someone knows an Asterisk solution for this?

-- 
Daniel