okeedokee, you're right. It's not a MAC address problem.
my prob registering with the other proxy servers seem to stem from my crappy ISP not knowing about their servers. the default setting when the ATA is provisioned is to do parallel lookups between the manual set DNS servers (BV specific) and the DHCP ones assigned locally from my router. This would explain why sometimes my ATA would be registered and others I couldn't get a dialtone.
I changed it to manual only and no more problems connecting to any of the broadvoice proxy servers.
I also re-enabled the YES option for provisioning just to see what it would make line 1 use on my SPA-1001. It was set to
proxy-dca.broadvoice.com
which seems to be an internal only server known only to the broadvoice.com domain DNS servers.
doing a dig or nslookup pointing to my local ISP servers doesn't recognize it
anyhoo, my vmail greeting and proxy probs are fixed for now.
BV customer support said that they have issues with the chicago proxy server and still haven't fixed that yet. So in the meantime, I'll continue pointing to a different server