You didn't specify if you're doing this for network cabling (Cat5, 5e, 6), or for telephone (analog or digital), or something else entirely, so I'll have to guess.
So I'd say that for network connections, you're likely to cause reflections on the wire, which will effectively shut down that connection by appearing to be collisions.
For analog phone equipment, you're probably safe.
For digital phone equipment (Nortel, Lucent, etc.), I don't know enough to answer one way or another, but I'd say try it with a test circuit that won't hurt anyone's access, and then you'll know.