BluPhenix, In thoery I agree with you but in practice my experience is quite different. As long as the RS232 speed is 56K or less I have never seen issues with noise pickup using unshielded cable. As a common practice I have run phone and LAN in the same cat 5 cable (100 base T service) and suspect I could have run LAN and RS232 with no issues but have never had a need to do so. I have run LAN and IR many many times with no issues and IR runs a ~40khz carrier at 5-12 volts.