I have a phone line on a CAT5 with data and I haven't noticed the noise but I am deaf.
(Too many years around line printers and check sorters)
The problem I have heard of is ring current spiking the LAN and causing errors. I don't have any "bell" ringers so I doubt it is a problem. You probably wouldn't notice the errors in a residential setting anyway. If you were in an office where the LAN was banging hard all day and the phone never stops ringing it might be significant.
