Does anyone know what Cisco's official stand is on using Cat3 cable for VoIP in 2009?
er - guys,
while I would never recommend that a client run it - Cisco does support it. From the CCM 7.X SRND:
Category 3 Cabling
The use of Category 3 cabling is supported for IP Communications under the following conditions:
•Phones with a PC port and a PC attached to it (Cisco Unified IP Phones 7975, 7971, 7970, 7965, 7962, 7961, 7960, 7945, 7942, 7941, 7940, 7911, and 7910+SW) should be set to 10 Mb, full-duplex.
This setting requires hard-coding the upstream switch port, the phone switch and PC ports, and the PC NIC port to 10 Mb, full-duplex. No ports should be set to AUTO negotiate. If desired, you can hard-code the phone's PC port to 10 Mb half-duplex, thereby forcing the PC's NIC to negotiate to 10 Mb half-duplex (assuming the PC's NIC is configured to AUTO negotiate). This configuration is acceptable as long as the uplink between the phone and the upstream switch port is set to 10 Mb full-duplex.
•Phones with no PC ports and with 10 Mb switch ports (Cisco Unified IP Phones 7902, 7905, and 7910) should be allowed to auto-negotiate to 10 Mb, half-duplex.
Because these phones support only 10 Mb Ethernet and their ports cannot be manually configured, the upstream switch port should be set to either AUTO negotiate or 10 Mb, half-duplex. In both cases, these phones will negotiate to 10 Mb, half-duplex.
•Phones with a PC port but no PC attached to it (Cisco Unified IP Phones 7975, 7971, 7970, 7965, 7962, 7961, 7960, 7945, 7942, 7941, 7940, 7912, 7911, and 7910+SW) can be allowed to negotiate to 10 Mb, half-duplex.
If you leave these phones with the default switch port configuration of AUTO negotiate and configure the upstream switch port to 10 Mb, half-duplex, these phones will revert to 10Mb, half-duplex.
Note The Cisco Unified IP Phone 7912 should not be used with Category 3 cable when a PC is attached because the switch and PC ports on this phone cannot be forced to 10 Mb, full duplex.
My friend Paolo is most correct (+5 buddy!)
Here is a clip from an "old" Cisco doc;
There is limited support from Cisco for using Cat3, have a look;
Q What type of Ethernet cables can/must be used?
A We support all standard cable types.
CAT3 Supported for 10Mbps
CAT5 and above Supported for 10/100/1000Mbps
The link between a bus and a drop cable that connects a workstation to the bus.
Category 5 (CAT5) cables support frequencies up to 100 MHz, while Category 3 (CAT3) cables support frequencies no higher than 16 MHz. For this and other reasons, CAT5 is an increasingly popular choice, especially in networks that carry both data and voice traffic.
Hope this helps!