[Aaug] 2 ATAs one extension

[cfowler]

I thought that it was possible to have 2 ATAs registered to the same
server with the same extension.  I tried this today with 2 offices.
Placing a Sipura-2000 in both with the same extension of 301.  When we
dialed 301 the phone at my home office rang but the one at my desk did
not.  I came to the conclusion it was because I had 2 phones registered
with the same extension and that is not a great idea.

What is the best solution for this problem?  I thought that maybe
301 should be the extension number for a ring group that points to the
ATAs at 30100,30101,30102,...  Everyone else thinks my real extension is
301 with mailbox at 301 but when 301 is called a ring group is called to
talk ring these phones.  I think the only downside is that the CID on 
the phone of the person I dial will see 30100 instead of what I want them
to see as 301.  Is there a cid option I can set under the extension of
sip.conf?