These numbers are called short codes. There is an organization called the common short code administration or CSCA that gives these numbers out. They are kind of like Internic (network solutions) was when domain names were first sold.
The cost is $1000 per month for the short code you want and you have to apply for it through the csca website http://www.usshortcodes.com/
You will then need to find 4 different providers to help implement your program.
A content provider - Content providers are typically large and well-known media organizations, advertisers, and consumer product companies. They develop and/or sponsor programming or promotions with which end users can interact via common short codes. They are the companies that own the brands or have license to the content published through the application.
An application provider - specialize in software development and hosting for mobile messaging applications.
A Connection aggregator - allow you to obtain connectivity to participating wireless service providers' networks so that a message addressed to their CSC can be routed from the wireless network to their application.
A wireless service provider - these are the wireless communications companies you know, such as at&t, t mobile, verizon
For more info visit the CSCA website
http://www.usshortcodes.com