At what point in the cycle of a cold does one become non-contagious?

There really is no definitive point at which a person with a cold becomes non-infectious. Colds are carried by different germs, so it would be hard to tell which exact one it is, and how long, or how much of the organism is needed to infect someone else. Sneezing or coughing into ones hand, then touching surfaces like phones, doorknobs, keyboards, etc., can still leave enough germs for someone else to incubate. Best bet is to cover ones mouth and wash their hands frequently.