Scott,
By default You cannot reach the extensions registered to SPA9000 from the extensions registered at Openser. You will only reach the SPA9000 line registered at Openser. You can reach the other extensions registered at SPA 9000 if the SPA9000 line registered at Openser forward the call to the other extensions or if you set the extensions on SPA9000 to receive calls without authentication but for that to work you need to create aliases for that extensions on Openser pointing it to SPA9000
Regards, Juliano Duque