By Andrew Mikesell

Each geographic market contains more than 1,000 models of mobile phones. Releasing mobile commerce applications for Android, BlackBerry and iPhone devices may cover a large proportion of your target audience in developed markets. However, in emerging markets where smartphones are the minority, you need a different strategy.

In developing regions, the question is not for which smartphones you will build an app, but which mobile technology works best for your app and users.

There are three protocols to choose from: SMS, Unstructured Supplementary Service Data (USSD) and Wireless Access Protocol (WAP). In addition, the SIM Toolkit (STK) lets you add new functionality to feature phones.

SMS
SMS, or text messaging, is the oldest of these technologies and the most widely used.

SMS messages can transmit one-way ?push? notifications such as alerts, news, offers and other data from content providers to subscribers.

In addition, SMS can carry binary data, so it can be the wireless delivery mechanism for downloads such as ringtones and operator logos as well as encrypted messages.

SMS also supports two-way interactive messaging, including allowing bank accountholders to check their current account balance by texting ?BAL? to a specific phone number or short code.

The main advantages of SMS are its ubiquity and ease of use: it is available everywhere and is accessible to all end-users irrespective of their wireless carrier or mobile device type.

The main drawback of SMS is lack of encryption.

SMS services cannot use Personal Identification Numbers (PINs) for authentication, because copies of messages are stored in the unsecured Sent folder. This limits SMS to services that do not require authentication or that require the PIN to be requested ?out-of-band? in another medium, such as by an Interactive Voice Response (IVR) call to the subscriber to request the PIN.

While Multimedia Messaging Service (MMS), or picture messaging, is widely used in some markets, it is generally not used in mobile commerce services.

MMS is costlier than SMS, and controlling how it appears on the device is difficult. One exception is MMS for bar codes, but this is still a niche use.

USSD
USSD is nearly as old as SMS, but is available only for external services in a limited number of markets.
Where it is available, which includes parts of Africa, Central America, Europe, India and Southeast Asia, it is generally very popular.

Unlike SMS, USSD establishes a real-time connection that allows for true session-based communications. Think of it as the mobile version of IVR systems that many companies use for customer service?but without the voice.

Like SMS, USSD can transmit push notifications, answer queries from users ? the available balance in a prepaid mobile account ? and top-up the balance on prepaid mobile accounts.

Also like SMS, USSD is accessible from virtually any mobile phone, and using it is easy.

A big advantage of USSD is that it can incorporate secure password or mobile PIN protection, because sent messages are not stored on the device.

USSD does have drawbacks.

Charging for services is difficult because carriers do not have a built-in billing mechanism. It is not guaranteed to work when you roam. And your phone must be turned on to receive messages.

When your phone is off, out of range or in a dead zone such as inside an elevator, you will not get the message?and unlike SMS, USSD provides no ability to resend messages.

For those reasons, USSD is not a good option for services such as fraud alerts.

If you launch services in a market with USSD, it provides maximum reach. However, USSD requires the carrier to make it available to external services, so this limits its availability.

WAP/Mobile Web
Using XHTML ? a variation of HTML ? for mobile Web access, WAP 2.0 has been available on most feature phones since 2004. Since the launch of iPhone, most smartphones have supported browsers that support HTML.

WAP 2.0 provides a mobile experience much closer to a desktop and laptop Web experience than the original WAP standards did, but it is still different enough that a WAP experience and Web experience will not be exactly the same.

A WAP user experience can be close to what you get with a basic mobile app. WAP does not have access to the mobile phone?s features like an app does, but it is still a good back-up plan for users without smartphones.

STK
Using SIM Toolkit (STK), developers can build an application that is stored on the Subscriber Identity Module (SIM) card and appears in the top-level menu of a feature phone.

STK allows these apps to request and receive information from SIM, give commands to the mobile device, ask for input from the user and communicate with external applications.

A few services use STK for mobile banking and other kinds of apps with simple interfaces and a low level of functionality. The main benefit of STK is security in the form of identity verification and encryption.

From a security standpoint, giving subscribers an STK application is like giving them a dedicated terminal.

STK is ideal for financial or mobile commerce deployments where customers have access to a network of cash-in/cash-out agents, such as those of the M-Pesa system in Kenya or in other peer-to-peer markets where subscribers trade airtime.

The challenge of STK is that it usually requires the carrier to issue a new SIM card. For that reason, it is best to use STK in limited distribution environments.

Word about alerts
With all the sophisticated technologies available today, is SMS still needed? Will we eventually replace its most popular function, the alert, with the alerts available on Android and iPhone devices? Not necessarily.

Depending on the importance of your alerts, even if you are rolling out a smartphone app, you may want to maintain SMS for certain types of notifications, such as fraud.

IPhones running iOS5 and Android devices display alerts in the status bar/alerts center of the device. These alerts are perfect for simple service notifications such as ?You have two new comments on Facebook.?

However, because users are accustomed to receiving many alerts, and on Android you can only clear all alerts, Android alerts may not be the best choice for important messages.

For key mobile commerce alerts, such as payment due or fraud notifications, alerts on Android devices risk not standing out or being cleared in error. In cases like these, using an SMS for the alert can be preferable.

With SMS, if you clear the alert, you can still go back to your inbox and read it at your leisure. You can reply to it, if you need. Plus, SMS alerts can contain clickable URLs.

Right technology
When launching a mobile commerce service, most clients want a tiered approach to the devices they will support. They might build a set of smartphone apps for Android, BlackBerry, iPhone and Windows Mobile, then have a WAP option for a middle-of-the-road user ex¬perience plus an SMS option for guaranteed connectivity.

In countries that have it, USSD may be a better choice than WAP.

The landscape of mobile technologies is complicated?and constantly changing. Companies planning to build applications should research the options and work with a knowledgeable partner that can make reliable recommendations based on the target market and services offered.

Andrew Mikesell is product director for mcommerce at Sybase 365, Boston. Reach him at .