What are the size limitations of a text message?
Standard text messages are limited in size to 136 characters.  This includes all letters, numbers, symbols, spaces and punctuation.
 
What does it mean to Opt-in? What is a double opt-in?
Opt-in means to join an alert. The customer gives you permission to send SMS messages to their phone.  Users send a text message to a keyword to “opt-in” to the database of mobile alerts.  A double Opt-in is a confirmation of a subscription by requiring users to respond a second time to confirm their subscription.  
 
What does it mean to Opt-out?
Opt-out means to quit a SMS alert.  Users send a text message to a keyword to “opt-out” of the database of mobile alerts.  The operators/keywords for this are usually “stop” or “quit.”  It is recommended that a supplier send no more than one or two messages per week to subscribers – more frequent messaging can result in higher opt-out rates.
 
What is a "Premium" campaign?
Premium-SMS campaigns charge the end-user (customer) for receiving a message, or a group of messages.  Examples include "joke of the day" and ring tone campaigns.  In most cases the user is charged a monthly fee (example: $5.00).  The fee is charged and collected by the carriers and the revenue is split between the carrier and the company orchestrating the campaign.

 

What is a Keyword and Short Code?
A Keyword is a phrase that users can text to join.  A Short Code is a series of numbers that act as a URL for a website. It tells the wireless carriers where to send the message. Similar to an abbreviation, the 5-digit code is easy for your customers to remember.

 

Keywords and Short Codes work together to form an address. Example: Text [KEYWORD] to [SHORT CODE] to receive a particular offer or to sign up for a particular alert.