For a lot of people, Short Message Service (SMS) was their introduction to mobile marketing. Before push notifications, before you could easily check email on your phone, before smartphones really existed—back when talking about in-app message would have made people go, “Sorry, in-what messages?”—SMS was pretty much the only way to reach customers on their cell phones.

SMS text message that evolved out of standards for text-based communication for mobile devices back in the mid-1980s. But while virtually all phones on the market—smart- and otherwise—currently support SMS, and the technology is still widely used by consumers to communicate with friends and family, it’s not a well-thought-of marketing channel anymore. That’s partly a result of the way SMS was used in marketing in years past: scattershot, invasive blast messages that few people were interested in receiving. That legacy, along with other concerns (Too invasive! Too tricky! Limited format!), has made a lot companies leery about using the channel.

While you’ll sometimes see brands using SMS as part of the customer engagement mix, most companies have replaced this channel with other mobile-focused messaging methods—particularly push notifications. It’s unlikely that SMS is going to be central to your customer outreach today, but there are some situations where it can be a smart way to communicate with your audience. To help you figure out when and whether to take advantage of SMS, let’s dig a little deeper:

The cons of SMS marketing

1. The cost factor

While the vast majority of people in the United States now have unlimited texting as part of the phone plans, there’s still nearly a 10% chance that when brands send a marketing message to a customer via SMS, that recipient will be charged. And while some users may shrug off that cost, paying to receive a message isn’t something that many customers will take kindly—especially if they don’t find the message relevant or valuable.

2. No support for rich content

With SMS, you just get words: no color, no pictures, no video. For some messages, that’s just fine. But this limitation puts SMS at a notable disadvantage to its closest mobile outreach cousin, push notifications. While push are often seen as being text-only, too, the truth is that the introduction of iOS 10 made it possible for brands to send notifications that include rich content like pictures, animated GIFs, video, and more. And that support can make a big difference—for instance, just adding an image to a message has been shown to increase conversions by 57%. That’s a functionality that SMS just can’t match.

3. Copy lengths have strict limits

While push notifications tend to perform best when they’re short, that channel does have the ability to support different amounts of text, in addition to rich content. SMS messages, on the other hand, have to be no more than 160 character, limiting what messages can be conveyed through this channel.

4. Can be seen as invasive

One side effect of SMS marketing predating other mobile channels is that it’s often lumped in more with traditional telephone marketing, rather than with email and in-app messages. And, like phone marketing, SMS outreach is often seen as invasive, rather than welcomed. That may be because these channels are generally used by consumers to communicate with friends and families, rather than brands, making it disorienting and unpleasant when brands try to take advantage of it. That’s an issue faced by OTT messaging platform chatbots, too—which may be why Facebook decided to require customer to opt-in to receive messages from brands.

5. May be duplicative of push notifications

If a customer provides you with their phone number and opts in for push, you have the ability to send them both a SMS and a push notification when you have something urgent to tell them. But if you use both in concert, you run the risk of annoying them with messaging experiences that feel duplicative. You want them thinking, “Okay, good to know,” not “Wait, didn’t I already get this message?” If you’re going to send someone a push, think twice about sending them a SMS, too.

The pros of SMS marketing

1. Messages stick around

While most customer outreach is very much of-the-moment, there are some kinds of client communication where you need the messages to stick around. That’s especially true for transactional messaging—think receipts, think password reset notifications. When you send push notifications, they disappear when a user taps on them, but SMS messages will continue to be available until they erase the outreach or switch phones.

2. Supports easy two-way interactions

Some messages don’t need a response—a receipt, for instance. Others are intended to drive recipients to a brand’s app or website. But if you’re sending a message to your audience that is intended to kick off an ongoing two-way conversation between customer and brand, SMS is well-suited to carry it out. For instance, letting you know the wait time for a table at a restaurant after you put your name in (and letting you cancel via text if that wait’s too long).

3. Allows urgent messaging without push opt-in

There aren’t a lot of messaging channels well-suited for genuinely urgent messages. If you send an email, recipients might not check their messages in the relevant timeframe; if you send an in-app message or create a News Feed Card, they’ll need to open your app or website to see it. Push notifications are ideal for this use case, but what if a customer has opted out of push? SMS can be a stand-in for push when communicating with those users—but be thoughtful about how you use it and how often. After all, a customer who opted out of push because they received too frequent or irrelevant messages isn’t likely to welcome SMS outreach that makes the same mistakes.

4. Lets marketers reach customers who don’t have smartphones

While 77% of people in the U.S. now have a smartphone, there are still millions of Americans using flip phones—and that’s not counting the billions of potential customers around the world who don’t have access to smartphones or tablets. Push notifications can’t reach people on their flip phones, but SMS can, giving it a potential leg up among these users. However, think carefully before building out SMS campaigns for this audience. Because the internet connectivity on most flip phones is so basic, using SMS to drive these users to your website is likely to be an exercise in frustration, reducing the number of feasible use cases. If you need to reach an audience of people without mobile devices, it may well make more sense to leverage email or web push in order to drive them to a desktop web experience that’s genuinely appealing and valuable.

Keep it cross-channel no matter what

The bottom line is that while SMS can be an effective way to reach customer in certain situations, it should never be your only marketing channel. There are things you can’t say effectively and people you can’t talk to successfully this way. Plus, even if you wanted to go all-in on SMS, you’d need some way of convincing people to sign up for text messages. Ultimately, it’s all about finding a good fit in your cross-channel marketing strategy—use SMS when it makes sense for the use case and the audience, not just because it’s there.