Be aware that telephone numbers can stick around for years and years. If you actively promote your company and widely publicise your telephone number, then expect it to be found in lots of strange places years after you think it is dead. Years ago when I was running a campaign for a major retailer, I was surprised that one of our agents was quoted a reference code from a promotion that was 6 years old – the information was in a very old magazine that someone picked up 10,000 miles away, liked the advert and called. This is not unusual. When considering changing numbers, consider where your number may have been promoted and through what media – if it’s magazines, books, etc then it will have a long lifespan, if its on TV it will be short. So keep your old number just in case someone calls!