how to start a short code service (like 5555)?

What you need to do first of all is be more specific. What are you talking about by "short code service"? I doubt you mean Morse Code, but beyond that I have no idea. Is something people would dial? Would this be on a traditional land line switched PBX, a more modern VOIP, or cell phone, or something else? You need to specify the environment.

I presume you mean a shortcode that mobile phone users can send SMS and MMS messages to.

The CTIA manages short codes through their web site at

If you pick your own short code, they cost $1000/mo, if you let them pick one it's $500/mo. The minimum term is 3 months, payable in advance.

Once you have your short code, you have to arrange with the mobile carriers to make it work. There are service bureaus that do this which you can find with Google. Again, you're going to have to pay thousands of dolllars to get set up.

There's two different kinds of SMS and MMS, normal and premium. Normal ones are just like any other SMS or MMS, and cost the user whatever a SMS or MMS to another mobile user would cost. Premium are analogous 900 numbers and cost the user extra, both inbound and outbound. Like 900 numbers, they are a business full of slimeballs and I would encourage you to stay away from them.