SMS Overview

About Short Message Service

Colloquially known as “text messaging,” Short Message Service (SMS) uses standardized communications protocols to allow web applications, mobile devices and text-enabled landlines to send and receive typed messages.

All messages are delivered either via A2P or P2P route with a registered code or mobile number for routing and tracking purposes. Depending upon route and country, the supported sender ID (code, mobile number, etc) type will vary.

Quick Facts

  • Message Length: Standard, plaintext SMS in the U.S. have a max limit of 160 characters per message. This limit varies by handset, country and message content.
  • Concatenation: Some carrier networks support concatenation, which shortens the length of an individual message and chops it into segments, but stitches the content back into a single message for the end-user’s easy reading.
  • Message Content: characters can be letters, numbers or an alphanumeric combination. Non-text based SMS (such as binary) are also supported.
  • Delivery Status: Due to the nature of store-and-forward technology, it is possible to receive notification of a message’s arrival at various stages in its delivery process.
  • Consumer Reach: All end-users whose mobile devices support SMS can participate in SMS messaging.


  • There are more mobile phones on planet earth than any other electronic device.
  • Mobile users can receive SMS messages even when they can’t get phone calls or access mobile data (like emails) because SMS are sent over the carrier’s own dedicated control channel. This makes SMS the ideal form of information relay during disasters.

Example Use Cases

Just a few common examples of SMS use cases include:

  • Account balance updates
  • Customer feedback surveys
  • Live Q&A
  • Loyalty & promotional deals
  • Marketing promotions and offers
  • One-time password conveyance and 2FAuthentication
  • Product recommendation and selection
  • Reminders, alerts and notifications
  • Reservation confirmations & updates
  • Service notifications
  • Sweepstake and contest entry


Wireless carriers, service providers and regulators aim to protect consumers from unwanted commercial messaging referred to as SPAM. The players in the mobile ecosystem don’t want text message content to suffer the same fate as email, many of which go unread due to an overload of SPAM.

Though anti-SPAM filters are used on carrier networks around the world, the governing bodies in the U.S. and Canada promote anti-SPAM best practices and enforce anti-SPAM regulation more stringently than any other countries globally. Most crucially, the U.S. FCC’s Telephone Communications Protection Act (TCPA) and Canada’s Anti-Spam Legislation (CASL) require all commercial messages receive consent prior to sending messages to end-users. Due to the abundance of North American messaging stipulations, you can find many articles here on Aerialink Documentation dedicated to the topic of U.S. and Canadian carrier compliance, certification and best practices.


The SMS-applicable rules adopted by the Federal Communications Commission (FCC) under the Telephone Consumer Protection Act (TCPA) became effective on October 16th of 2013. Aerialink advises all customers to discuss these regulations with their legal counsel and take any and all necessary actions to comply.

The purpose of the TCPA is to protect the privacy interests of phone subscribers. SMS messages are subject to these regulations. Section 227(b)(1)(A) of the Act specifically protects wireless users, among others, from auto-dialed or prerecorded “calls” (that includes mobile messages) to which they have not consented.

These Federal rules apply to marketing-related content for all SMS and MMS routes as well as phone call telemarketing and are not mobile carrier, CTIA, or MMA-regulated. It is therefore up to each individual customer to implement these rules to comply with the FCC. Failure to comply with any and all revisions to the TCPA could result in federal investigation.

The following is a list of the requirements which must be met by mobile programs in order to satisfy the FCC TCPA.

  1. Opt-In: Express “written” consent is obtained prior to sending messages, and only after clear and conspicuous opt-in instructions have been provided which detail the method and circumstances under which the user is providing their consent so that all end-users are completely aware of what they are agreeing to.
  2. Consent Records: To protect your organization from future disputes, it’s advisable to maintain each contact’s consent for at least four years from that date in which it was given, which is the federal statute of limitations for bringing an action under the TCPA.
  3. Opt-Out: Clear and accessible unsubscribe instructions must be provided.
  4. “Do-Not-Call”: A record and listing of opted-out users must be kept for a minimum of four years, during which time those users cannot be contacted.
  5. Dark Hours: Messages cannot be sent between 9pm and 8am at the subscriber’s local time. (If your service sends messages to users in different time zones, contact your account manager about the various options we can provide to manage this requirement.)
  6. “Consent is not a requirement of purchase,” must be stated either at point of opt-in or in a Terms & Conditions page linked from that opt-in point.(see below)
  7. Terms & Conditions: All mobile programs must provide a mobile messaging T&Cs page.

There are two crucial points to consider with regard to obtaining consent.

  1. Content Providers, Sellers, etc. can no longer rely on “Established Business Relationship Exemption” as a basis for making robocalls and prerecorded telemarketing calls without prior express “written” consent.
  2. “Written” consent must be obtained.

Regarding compliance with the E-SIGN Act, form of “written” consent:

“Because it greatly minimizes the burdens of acquiring written consent, commenters generally support using electronic signatures consistent with the E-SIGN Act. We conclude that the E-SIGN Act significantly facilitates our written consent requirement, while minimizing any additional costs associated with implementing the requirement.”
(FCC 12-21 section 34)

All methods of obtaining consent must adhere to the above guidelines by providing clear opt-out instructions and access to relevant information. They must be presented to the end-user clearly and conspicuously, and the end-user must be aware that they are not required to consent in order to purchase goods or otherwise interact with your business. The following methods of obtaining consent are therefore acceptable:

  • SMS*
  • Web Form or Widget
  • Mobile App
  • Digital Signature
  • Paper
  • IVR
  • Verbal via phone
  • Verbal in-person

**While most use-cases will utilize keyword-initiated SMS consent, organizations qualifying for exemptions to the “established relationship” ruling, such as Non/Not-for-Profit organizations, may send “invitation” messages to existing contacts. Please see the TCPA report for a list of applicable exemptions.

Monetary Fines

According to the TCPA Rules, violators may have action taken against them in a court of law for:

A. actual monetary losses suffered by the plaintiff as a result of the violations
B. $500 in damages for each violation.

Additionally, those found to have willfully or knowingly violated the TCPA or its prescribed regulations may be additionally fined - at the court’s discretion - for up to three times the amount available under item B.

SMS Technology

Store and Forward

SMS is a “store-and-forward” service. This means that before messages arrive at the destination handset, they are first routed through an SMSC—a Short Message Service Center. Networks, carriers and aggregators who support text messaging have one or more SMSCs to serve this function. If the mobile device is powered off, has a weak signal, is out of range or otherwise unavailable when the SMSC attempts to forward the message, the SMSC will store the message and continue to retry the message send until the end user receives the message or the retry period expires.

The reception of an SMS does not interrupt the mobile user’s voice calls or data usage. While those features require the use of a dedicated radio channel, text messaging utilizes a signaling path that bypasses the radio channel and its traffic clutter.

Network Technologies

The three primary wireless network technologies—GSM, CDMA and TDMA—all support SMS. GSM is the most widely used wireless technology in the world, with a market share of more than ninety percent. AT&T’s and T-Mobile’s infrastructures both use the GSM network, while Verizon and Sprint rely instead on CDMA.

Because these technologies are configured at the network operator level, differing configurations can cause variances in the behavior of SMS delivery. The specs and standards supported by the technologies also differ, but the delivery success of plain-text SMS remains very high.

The implementation of SMS differs depending upon the sender ID used and the route (A2P or P2P) chosen to carry the message traffic.

  • API: REST over HTTP, SMPP 3.3, SMPP 3.4
  • Carriers: United States, Canada, International
  • A2P Route: Available via shared or dedicated short code or via alphanumeric ID outside of North America
  • P2P Route: Available via U.S.-registered, local and international long codes
  • DLR: Supported
  • Incoming Keyword Matching: Supported

Launch Time

For dedicated short codes, the certification process takes eight-to-twelve weeks in the U.S., and three-to-six weeks in Canada. Shared short codes have a much quicker implementation time, requiring keyword commands unique to the program and not used by other Aerialink customers. U.S. P2P programs require Aerialink review and approval, but a long code program can be up and running in minutes.

This page was last updated 1515185923000