VOIP phones often have 10megabit interfaces on them. The reason why is so that they will work over Cat3 (or twisted pair that predates Cat3 but will still work with 10baseT such as AT&T DIW).
This is the biggest issue with Cat3, IMHO...non-managed switches and ethernet interfaces that autonegotiate to 100megabit. Cat3 works just fine if you manually set the port to work at 10megabit, but that isn't an option if you've connected two non-managed switches together. In that case they'll autonegotiate to 100megabit and this may or may not work over a cat3 link (will if it's short enough).
Otherwise..the average home user isn't going to notice a speed difference between 10megabit running on cat3 and 100megabit running on cat5 (or cat5e).
