Please, really do some internet or trustworthy book research on this before you run out and start buying infant cereal.
All the trustworthy books and websites will tell you that feeding your child cereal will NOT make him/her sleep though the night longer. If your child is under 10 pounds he/she NEEDS to eat once during the night. If over that, he/she has enough weight to be able to sustain though the night without a feeding. If your child is experiencing a growth spurt, no amount of cereal will prevent them from waking up hungry.
One of the many reasons its not recommended to start feeding your child cereal so young is because of calorie (and nutrient) density. This is the amount of calories (or nutrients) per gram (or other mass unit) avaliable. For example, protiens provide 4 calories per gram, alcohol provides 7 calories per gram, and fat provides 9 calories per gram. Alcohol is more calorie dense than proteins - but not as calorie dense as fat.
For babies, their stomaches are small so the more nutrient and calorie dense the food, the better. Formula and breastmilk are actually more nutrient and calorie dense than cereal (researching will tell you this also) - so your child is less likely to get hungry if he/she eats more calories. This alone is the primary reason why peds will recommend waiting until 4-6 months, but there are other reasons, too.
Studies have shown that the earlier children are fed cereal before 6 months, the better the chances your child will face overweight problems later in life. These aren't HUGE odds, but significant enough to warrant noting - let alone food allergies and digestion problems later in life. There are many many reasons why it's recommended you wait til at least 4-6 months, dr's aren't pulling a number out of their head to be jerks.
The point is, please just do some more reasearch on this before you make a decision.