Both Deven and Mark are correct here. The Novell DHCP server administrator probably defined the Option 150 that tells a phone how to reach CUCM at a global level instead of only within the scopes that cover the voice subnets. They can certainly change that if they feel like it; even Microsoft supports it and any modern Novell install is running on SUSE which probably leverages dhcpd like any other GNU/Linux system on the planet.
Additionally, in the absence of DHCP 150, 66, or the rarely known about default DNS query a phone will default back to the last config it had in memory and use the servers defined there. In other words, even if the DHCP server isn't handing out a DHCP Option 150 at all, the phone will still register if it has ever done so before.
Lastly, as Mark was saying, the voice VLAN was only invented to prevent companies from having to redesign their entire network subnetting, including every statically assigned device, to deploy IP phones. Think about it for a moment: your /24 DHCP scope is 70% exhausted and you need to deploy 150 phones within that same network segment. Without a voice VLAN you would be forced to change the subnet for the entire network segment. It was a essentially a way to remove objections to VoIP originally; however, other decisions got made after that invention including that lazy brat AutoQoS. It bases the conditional trust model for physical phones off of the presence of an 802.1p CoS header which can only exist because of the Voice VLAN concept which introduces an 802.1q header.
