Asterisk Multihomed? Multiple externhosts?

Hi guys.

We have an Asterisk 1.2 setup with 2 nic’s. Currently we have the sip.conf as follows:

externhost=my.asterisk.domain (using dyndns service)

Can we have multiple externhost entries? Such as - externhost=my.asterisk1.domain; my.asterisk2.domain? Would this be the correct syntax?

We are using 2 ISP’s and would like to setup the system for multi-homed, both as a fail-safe and load balancing for outside SIP phone registration. We would also like to have the external SIP phones use the primary domain to register “my.asterisk1.domain” and use the secondary domain “my.asterisk2.domain” as a backup proxy on the phones.

Has anyone tried this and had it successfully work?

Thanks for everyone’s time!