This particular need is a pet peeve of mine, and I see some misinformation / misunderstanding among posts on this thread.
A) The two methods bjyoung mentions are perfectly valid processes, but do involve manually entering information on the handset itself, which quite frankly, should not be necessary and in larger installs across multiple sites becomes time intensive for something that should be able to be done automatically.
B) Using option 66 is like NOT using phone feature packs - UNTRUE.
Options 66 simply tells the handset where to go. We use it with Polycoms all the time on multi-site installations because when the handset is on a remote subnet (routed in the clear - no nat) it is unable to detect the Switchvox and needs to be told where to go. From there on forward the phone downloads its config file and other info from the Switchvox utilizing the phone feature packs and provisioning.
C) Even on local single building networks, we often have a data vlan and a voice vlan. The Digium Phone Networks is great - IF somebody tells the phone where to go first. However if you boot up the phone untagged in the data vlan, it will have no way to read those beautiful phone network configs without sombody keying info directly into the handset.
Note - You could use LLDP for this - but not every switch supports LLDP not every network design.
D) I am by no means a multicast expert, but I thought maybe there might be something to the idea of setting up multicast for mDNS so that remote sites. After an hour or so of a crash course I discovered and verified through multiple sources that multicast group addresses in the 126.96.36.199 to 188.8.131.52 range are restricted and reserved - routers are not to forward these packets beyond the local subnet. MDNS is 184.108.40.206.
Google it up and you'll see alot of network engineers complaining about Apple/Bonjour. Apparently Bonjour/mDNS is all good and finme for tiny single-subnet networks, but really falls apart on anything even moderately complex.
Unless I'm missing something major, I'm not convinced mDNS was a great choice.... but like I said, I'm no multicast expert.
Addresses in the range 220.127.116.11 to 18.104.22.168 are individually assigned by IANA and designated for multicasting on the local subnetwork only. For example, the Routing Information Protocol (RIPv2) uses 22.214.171.124, Open Shortest Path First (OSPF) uses 126.96.36.199 & 188.8.131.52, and Zeroconf mDNS uses 184.108.40.206. Routers must not forward these messages outside the subnet in which they originate.
In short: supporting DHCP 66 as a means of telling the handset where to find the Switchvox when it is not immediately available be of tremendous value. In truth, I think I would actually prefer a custom DHCP option since 66 is often used by other devices (including Polycoms). This could allow a handset to be unboxed and plugged in anywhere on the WAN (including over VPN's) and because it would be able to automatically retrieve the "Phone Network Configurations" there would be no need for manual configuration - especially if this is combined with Digium's new feature to manually enter or import the MAC address <> Extension mapping.
EDIT: Oh and by the way, despite how it might sounds, I really do like the Digium phones and sell them almost exclusively now. I just want a way for my techs to be more efficient in deployments.