The indicated lengths of handset cords are for when the cords are stretched out, not when they are in their packages.
It's not comfortable to use cords when they're stretched to their maximum, so pick an appropriate length.
A 25-foot cord is suitable for walking around a room. It's the most popular length for kitchen wall phones -- and the least popular for office phones, because it makes a mess on a desk. Un-stretched, it's about about 36 inches long.
A 12-foot cord is suitable for walking around near a desk or standing near a wall phone. It has become very popular for office phones and is often the right length for a cashier at a restaurant. It's also good if you have a king-size bed. Un-stretched, it's about 17 inches long.
A 6-foot cord is suitable for sitting at a desk or lying in bed (single, double, or queen-size) when the phone is on the night table. Un-stretched, it's about 12 inches long. It's the standard length handset cord, supplied with most phones.