I've tested the linksys phones on a Catalyst express switch. The switch recognizes the phone and is put in the voice vlan, when I plugged in a SNOM phone, it was put in the data vlan. Both phones are running SIP protocol. How does the switch recognize a SPA508 when it's in SIP mode, I thought that it was SCPC that was sent to "tell" the switch that the phone is a phone?!? :)
This has to do with the fact that Linksys and Cisco phones support the Cisco Discovery Protocol (CDP), which is used, among other things for VLAN configuration. This protocol is also supported by the Cisco Catalyst and ESW switches, so when a phone or any CDP enabled device is plugged in, the right VLAN is assigned depending on the device type. This ease configuration.
Hope this helps