Phone Make and model from Serial number - How?

[etester]

I noticed that a few companies offer a service that identifies your cell phone make and model by entering in the serial number of the phone.

How is this done? ie: is there some sort of algorithm or web service that can be used to get this information?

For example through Vazu.com ( https://www.vazu.com/
) , you can send an SMS message with contact info that will be added to the contacts on your phone.

How is this done?

[SNSE]

Blocks of unique ESN's or Electronic Serial Numbers are allocated by manufacturers. Amongst the industry, they usually dedicate so many serial numbers to a particular model knowing how many they intend to produce. For example, ESN's starting with 39 (27 Hex) is an LG Phone. I would not go around entering my ESN into any website. Fraud is bad enough, let alone going around entering the phone's unique identifier to the masses.

Also, they can identify what carrier the phone went to, say out of a lot of 15,000 phones, there will be a specific segment of numbers that the manufacturer knows were dedicated for distribution by Verizon, or other carriers.