I read from this site http://www.javvin.com/protocolVLAN.html:
Many NICs for PCs and printers are not 802.1Q-compliant. If they receive a tagged frame, they will not understand the VLAN tag and will drop the frame. Also, the maximum legal Ethernet frame size for tagged frames was increased in 802.1Q (and its companion, 802.3ac) from 1,518 to 1,522 bytes. This could cause network interface cards and older switches to drop tagged frames as "oversized."
My question is if this type of problem pertains to antiquated NICs or if computers/printers bought within the past few years would certainly support "oversized" VLAN frames? I am planning to segregate our office network into VLANs (to optimize VoIP traffic) but I don't know if that means certain legacy devices will suddenly lose connectivity due to increased frame size.
Also, is there a way to test that a given device will support 802.1Q other than simply plugging it in and trying? (Note: I am familiar with Wireshark and could read ethernet frames off the wire if necessary.)