Recently I've noticed a number of companies like Jamster
(http://www.jamster.com), Comedy Central
(http://www.comedycentral.com/wireless/) and even Google
(://www.google.com/sms/) that offer services including jokes,
pictures, ringtones etc to their customers wirelessly.
The procedure is fairly straightforward: 
- You send a designated text message to a specified 5-digit-number 
(eg Google's is: 46645 / GOOGL & Comedy Central's is CCLOL)
- You receive your multimedia directly to your cellphone and your
cellphone account is billed accordingly (for paid services)

My questions is: 
1) How does one go about getting the 5-digit-shortcode & what is the
associated cost

2) How does the 5-digit-shortcode tie in with an SMS gateway

2) I've come across of a couple of SMS gateways, are there gateways that
handle both  multimedia transfer & cellphone account billing & what is
the associated cost per subscriber or sms message

3) Are these SMS gateways compatible with the major US cellphone carriers 
(primarily: Verizon, T-mobile, Cingular, Sprint/Nextel, USCellular, Alltell)

4) How do these services mesh in with pre-paid customer accounts.


Accepted answers will address the issues above and provide several
links to vendors as well as any online articles & forums with pertinent
information.

Thank you.

Unfortunately, no one at Google seems to know what an SMS Gateway is.
I tried to ask similar questions but only got ridicule in response.

Well, I'll probably just leave the question open for another week or
so, but thanks for checking in

1) How does one go about getting the 5-digit-shortcode & what is the
associated cost.

A. You can get a shortcode derectly from the Mobile carriers or thru
an Aggregator like http://www.mblox.com.  The carrier charges a flat
rate + % of sales.  The aggregator charges a higher % rate.  Carrier
$1000 per month + 60-75% of Sale price.

2) How does the 5-digit-shortcode tie in with an SMS gateway

You must setup your own SMS gateway that connects to the
carrier/aggregotor via HTTP protocol.

2) I've come across of a couple of SMS gateways, are there gateways that
handle both  multimedia transfer & cellphone account billing & what is
the associated cost per subscriber or sms message

At this point in the game there are not many "off the shelf" billing solutions.
Most of it must be written & coded in house.

3) Are these SMS gateways compatible with the major US cellphone carriers 
(primarily: Verizon, T-mobile, Cingular, Sprint/Nextel, USCellular, Alltell)

This fully depends on the carrier.  Some interface via HTTP, XML, and
others have thier own protocol specifications.

4) How do these services mesh in with pre-paid customer accounts.
This depends on the market, some countries / carriers do not allow
prepaid to be billed.

An alternative is to use a site like Phone Sherpa.  They have a
service that enables you to sell ringtones and wallpaper through your
own web store.  They provide a ringtone maker, wallpaper maker, all
the file hosting, billing, and delivery.  You get a percentage payout
depending on the store package...up to 45% of all revenue goes to you.
 Supports 25 countries and 120 carriers.  There are no monthly fees
either:

http://www.phonesherpa.com/sell_ringtones.aspx

You can take any mp3, wma, or wav files on your computer and use Phone
Sherpa's ringtone maker to convert your music into custom ringtones. 
They also have an easy to use wallpaper editor.  You can have your
mobile content store up and running in about 10 minutes.