SMS Messaging

OpenMarket's Global SMS messaging platform lets your developers create messaging programs for your specific needs. Here are the key capabilities you can leverage:


You can integrate with our SMS platform via HTTP or SMPP. Some of our customers favor HTTP because it is a less complex technology, while other customers favor SMPP to handle high-volume messaging programs. OpenMarket’s account managers are always available to help you decide. Both integration methods let you:

  • Send mobile-terminated (MT) messages to your end users.
  • Get the status of an MT message, up to five days after submitting it to OpenMarket.
  • Receive a delivery receipt that provides information about whether the message reached the handset.
  • Receive mobile-originated (MO) messages from your end users to your own system.
  • Look up which mobile operator services a specific mobile number, and get information about what messaging features the mobile operator supports.

One-way and two-way messaging

You can send one-way messages to more than 200 countries worldwide, and in many regions you can receive messages back for two-way messaging. If you need to only send messages and not receive any replies back, you'll want to use one-way messaging. Different mobile operators and geographic regions have their own behavior around one-way messaging. Things to know are:

  • Alphanumeric source

    In many countries (including the UK) you can set an alphanumeric string as the message originator, or source. This can allow you to brand the message as being from your company; e.g. "ACME SHOES". However end users cannot respond to a message sent via an alphanumeric .

  • Changing message sources

    When sending one-way messages in some regions, the mobile operator will change the source to a number of their choosing. This means that if you do wish end users to potentially respond, it is important to label the message as two-way.

  • Cost-effectiveness

    In some cases, one-way messages can be more cost-effective. Consult with your OpenMarket account manager for guidance.

To see where we support one-way and two-way messaging, see our SMS Global Coverage Map.

Two-way messaging

Use two-way messaging when you expect end users to respond to your message. Two-way messages must be sent using a short code or virtual mobile number (VMN) that's able to receive messages.

For a list of the countries where you can use two-way messaging, see SMS Global Coverage Map.

Note: All messaging in the US and Canada is two-way, regardless of whether you wish to receive responses. This is a regulatory requirement; the industry in these regions require you to send messages from a provisioned, text-enabled number.

Branded messaging

A branded message is a message that contains your company logo in addition to the message text. The fact that end users can see your logo lets them instantly recognize who sent the message, making it more likely to be read. Similarly, your message is much more visible in the end user's message inbox, making it easier to find and reopen.

To send branded messages your OpenMarket account must be configured with a campaign ID and you'll need to pass this in the message request. This tells our system to pass the request to RCS, which can determine which phone numbers are capable of receiving the branded message and which are SMS only. For details see Branded Messaging in What's New.

Support for all types of source numbers (originators)

Originator Type


Short code

This is a five- to six-digit number that works within a specific country. Short codes are popular with marketing and retail use cases, such as sending a message that lets end users opt in to a coupon program.

Virtual mobile numbers (VMN)

Also known as long codes and national numbers, a VMN is a standard mobile phone number. This type of source is often used for two-way messaging. VMNs do not necessarily work the same way in each country, so check with your OpenMarket account manager for details.


Due to their limited throughput (usually one message/second), long codes have been used traditionally for P2P messaging.



(US/Canada only)

A 10-digit long code is like a VMN but it's been specifically configured for A2P messaging in the US. Not all mobile operators support 10DLC.


See 10DLC is Here! for details, and stay in touch with the OpenMarket Blog for regular updates.

Text-enabled landlines and toll-free numbers

(US/Canada only)

Landlines and toll-free numbers can be text-enabled for both SMS and MMS. Using one number for all three channels is useful because your customers can more easily recognize and trust the number. For more information see Support for text-enabled toll-free numbers and landlines.


Not all mobile operators support use of toll-free numbers.

Alphanumeric string This type of originator is used for one-way messaging. You can use it everywhere except the US and Canada.

Automated originator selection

When sending messages to different countries, you'll likely use more than one source number. Since it can be challenging to select the correct source for each mobile number, our messaging platform can do this work for you.

With automated selection our system needs to know all of the originators you are using. With this information, all you need to provide in your 'send message' request is the destination mobile phone number. Based on that we determine the country and then use the matching source. If you use multiple sources for one region, we may need more information in order to choose the correct one for a particular end user.

Simplified character encoding

Choosing the right character encoding for a message and mobile operator can be confusing. With OpenMarket all you need to do is submit your message requests using UTF-8 encoding. Our system will convert the text content to use the encoding that's optimal for the mobile operator. For many mobile operators and messages, we use GSM.

If you're generating your message text using an encoding scheme other than UTF-8, you can still send us the text as is; you'll just need to use charset in the request body to specify the encoding.

Message concatenation

A message that requires only one SMS is called a single-part message. The maximum size of a single-part message may differ amongst mobile operators in different regions. In the UK and the US, a single-part message can be up to 160 characters (using the GSM character set) or 70 characters (using the UCS-2 character set).

Any message that exceeds the byte size limitation is called a multipart message. (Other terms include "long" and "concatenated" messages.) Multipart messages may require more than one SMS message. To work around the limit, mobile operators and handsets are able to combine multiple messages to form a single message experience for the end user. For example, if you send a GSM message of 500 characters to an end user in the UK, the message will be split into four parts and reconstructed as a long message on the end user's device.

Support for multipart messages is dependent on the region and mobile operator. Most operators support multipart messages of at least four parts. Some US operators support up to 20 parts. When you send an MT message request to us, we check whether the destination mobile operator accepts the message length. If not then we reject the message and send you an error response.

For more details, see Single and Multipart Messages.

Delivery receipts

Many mobile operators send back delivery receipts, which our system can forward to you so that you have information about whether the message was delivered to the destination phone number. A delivery receipt (DLR) contains the OpenMarket ticket ID that identifies the specific message and a code identifying the current delivery status for the message. A DLR can also contain custom information that you include in the original 'send message' request.

If a message is sent in multiple parts, then delivery receipts are sent for each part. Each part of the message contains the same ticket ID and each delivery receipt includes a 'segment number' so that you can track the status of the entire message and each part.

Operator look-up

Our SMS messaging platform enables you to send a message request with or without the ID of the mobile operator that services the destination phone number. If you do not include the ID, our system looks it up for you.


OpenMarket takes the security of your data very seriously. We work with a qualified independent security assessor to annually conduct third-party security audits across all our products. Our connections to mobile operators utilize industry-standard encryption technologies appropriate to the sensitivity of the information being transmitted. This means we use either VPN tunnels or SSL (TLS v1.1 or greater) to encrypt data being sent over public networks or private networks if required.

When you connect to us via our messaging APIs, you can utilize these security features: 

  • Use an HTTPS connection over secure port 443
  • Provide us with a whitelist of IP addresses from which we will accept API requests
  • Provide you with the OpenMarket IP addresses from which you should accept MO messages, delivery receipts and other notifications

See Authenticating with OpenMarket for more information.

GDPR compliance

OpenMarket is compliant with the General Data Protection Regulation (GDPR). In terms of information security and data privacy regulations, including the GDPR, OpenMarket is considered a data processor while our customers are considered the data controller. When you use our messaging APIs and end users’ data travels through our network, we process that data on your behalf.

OpenMarket has its own Information Security team and we utilize experts in the field of information privacy and regulatory compliance to develop our security review processes, build our security infrastructure, and implement our security policies. We work continuously to help you, as the data controller, meet your compliance requirements.

High availability

OpenMarket offers a "4 nines" SLA to ensure that our SMS services are highly available. We operate multiple data centers in different geographic locations, each one providing multiple hosts for connections and supporting 100% of the traffic load. In our geo-redundant architecture we provide one global endpoint for our SMS services; traffic is routed to the closest available data center. As such, traffic may tend to stay in one geographical region but it is not guaranteed.

Alternatively, you can load-balance your MT message traffic by connecting to multiple virtual hosts; however, if a virtual host becomes unavailable, you'll need to redirect traffic to a different, available host.

For MMS messaging, you also have the option of using a geo-redundant endpoint or connecting directly to the data centers.