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While text messaging occurs on cell phones, the SMS network is different than the network for voice calls. Unlike sending a few messages from phone to phone, sending texts to large numbers of people at once requires an interface system to send and track these messages.

Before launching into a full-scale SMS program, it is important for organizations to understand the technical, logistical and cost implications of text messaging interventions.

Life of a text message

Conceptually, sending SMS messages on a large scale has four steps. First, the user crafts a message to deliver to a recipient's, or multiple recipients' mobile device. There are several ways that messages are sent in this first step. Messages can be sent through mobile devices or web portals managed by service providers. In the second step, the message is submitted to the aggregator's SMS gateway.

The aggregator is an SMS service provider that acts as an intermediary between users, recipients and the mobile carriers. The aggregator locates the recipient's carrier and transmits the message to the carrier's Short Message Service Center (SMSC). The SMSC is the infrastructure responsible for sending and receiving SMS messages in a wireless carrier's network. The SMSC delivers the message to the recipient.

If the target recipient is not available, the carrier's SMSC stores the message until a later time for subsequent retransmission. Thus, SMS operates as a store-and-forward service unlike a voice call. Each carrier has different policies about how long they will hold a message, but after that period of time expires, the message is deleted.

Occasionally an SMS text message delivery is delayed, or not delivered at all, particularly if an end user's phone is turned off for an extended period of time. Some other causes are: network congestion, the destination handset is beyond the coverage area, the destination handset memory is full, or there are outages in the service provider or network infrastructure.

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There are hundreds of vendors that provide SMS services. How do you pick one? What questions should you ask before signing a contract? Our summary document provides a brief overview of SMS-based text messaging services offered by commercial vendors. It describes what capabilities different vendors offer, common pricing schemes, and some key questions to ask vendors when planning to implement a text messaging program.

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Texting 101: Chapter 3

The life cycle of a text message and working with SMS vendors. Enlarge video.


  • Basic concept
    You can send text messages one by one from your computer or your cell phone. However, if you have many people that you would like to reach by text, consider hiring a commercial vendor to assist in distributing the messages. The vendor will manage your database of cell phone numbers, and allow you to customize and time messages to groups of individuals within your database.

  • Opting in
    The vendor will set up a system by which your clients can opt-in (and out) of your text messaging program. Remember, to send a text message you must have permission which is assumed when a person opts in. No text "spam" is allowed by federal law.

  • Costs for users
    In the U.S., it costs to both send and receive a text message. The fee depends on the contract the user has with his/her cellular phone carrier.

  • Short Message Service ("SMS")
    SMS is another word for text messaging. Text messages can be 160 characters (including spaces) long.

  • MMS
    Multimedia Message Service: sending photos or video via text message.

  • Short code
    A five or six digit telephone number that is assigned to your text messaging program. People can send a text to this number to opt-in to the program and will receive your messages from this short code. You can use the vendor's shared "group" short code or have a dedicated short code assigned to you. A dedicated code is considerably more expensive then a shared code and takes longer to establish, but offers the purchaser a unique number.

Should you be your own SMS vendor?

OVERVIEW: There are a variety of options to consider when planning text messaging projects. Typically, a vendor provides a web-based interface into which subscribers' cell phone numbers are entered, along with the text messages you want to send. The vendor builds and manages the database, and links your messages with an aggregator or directly with the cell phone carriers for delivery. However, you can build your own application to manage some (or most) of this process. We conducted an analysis to compare contracting with a vendor vs. building some or all of the application yourself.

METHOD/PARTICIPANTS: ComGroup Inc. conducted the cost analysis in consultation with our texting team.

RESULTS: ComGroup Inc. came up with four options:

  1. Use a fully hosted vendor solution. Typically, you'll be provided with a web-based interface that you and your program administrators can use to input and manage subscriber lists, and schedule and send text messages.

  2. Commercial Off-the-Shelf (COTS) solution. Your agency purchases the application, develops or modifies the user interface and hosts the database. You house the physical infrastructure and servers needed to support the COTS application. This option requires professional services to customize the database, and internal resources to maintain the database. 

  3. Develop in-house SMS application. This solution requires internal resources to develop and maintain the recipient database. You own the user interface and database, and contract with an aggregator to transport messages to the carriers.

  4. Develop application and operate as an aggregator with direct contact with carriers.

Option one is the easiest solution. There are many vendors that offer a variety of services at different price points. However, customer service and interface flexibility are limited. Security and reliability may be an issue, depending on your agency's needs. For example, you may not be able to text clinic patients if you cannot assure the security of an off-site server and database. Options two and three provide the most control over the operation and management of the SMS system. However, your agency needs significant expertise in application development and database management. Investing significant time and effort in a technology that is ever changing also presents its own risks. Option four is not a feasible option for health departments. We were unable to find any municipal agencies that act as aggregators.

RECOMMENDATIONS: Our consultant found that Options 2 & 3 cost approximately 20% more than the first option, with an economy of scale being reached depending on the number of individual texting programs the department has. In addition, the relative flexibility and control over these options make them a good choice, depending on the ability and availability of Information Technology staff available. Option One is a good option for occasional smaller scale texting programs, particularly when staff are beginning to learn how to develop and run texting programs. Option Four is not a feasible option, in part due to its excessive cost (in excess of $4 million over five years.)

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