SMS (Short Message Service) is one of the most widely supported messaging channels on the planet. It’s simple, works on nearly every phone, and doesn’t require users to install an app.

That universal reach is exactly why SMS remains a default choice for onboarding, alerts, and time-sensitive notifications—especially when you need to reach a user who may have limited data access or doesn’t use a specific messaging platform.

At the same time, SMS comes with hard technical and security constraints that teams often underestimate.

If you’re building workflows for authentication, verification, support, or transactional messaging, understanding what SMS can and can’t do will help you reduce delivery failures, improve user experience, and choose the right fallback options.

1) SMS is “short” for a reason: encoding and length limits

A common assumption is that SMS supports 160 characters, full stop. In reality, the character limit depends on the encoding used. Many languages and emoji require Unicode, which reduces the number of characters that fit into a single message. This becomes especially important for global products supporting multiple regions and scripts.

• GSM 7-bit (common Latin characters): typically up to ~160 characters
• Unicode/UCS-2 (many non-Latin scripts, emoji): typically up to ~70 characters
• Long messages: are split into multiple segments, which can reduce per-part capacity

This matters because messages that cross the threshold are segmented and reassembled on the device. Segmentation can increase cost, raise the chance of partial delivery, and create confusing user experiences when message parts arrive out of order.

2) Delivery is best-effort, not guaranteed

SMS delivery is often reliable, but it is not deterministic. Carrier routing, congestion, device state, and regional filtering can all introduce delays or failures. Even when systems provide delivery receipts, those signals may not be consistent across carriers and devices.

For operational planning, it’s safer to treat SMS as a “best-effort channel” and design flows that handle:

• delayed messages (especially during peak network times)
• non-delivery for certain routes or recipients
• inconsistent delivery status reporting
• regional variability in filtering and spam detection

3) SMS is not end-to-end encrypted

From a security standpoint, SMS is fundamentally different from modern OTT messaging apps (e.g., Signal or WhatsApp) that support end-to-end encryption. SMS messages generally travel through carrier infrastructure in a way that can expose content and metadata to service providers and, under certain circumstances, other parties.

That doesn’t mean SMS is unusable—it means the type of information you send over SMS should be carefully considered. For example, sending full sensitive content via SMS is often a poor choice. Many teams instead use SMS to send short prompts and direct users to a secure in-app experience for anything confidential.

4) Practical guidelines for using SMS safely and effectively

If SMS remains part of your messaging stack, a few operational best practices can make a big difference:

• Keep messages short and clear: avoid segmentation; use concise language and minimize Unicode-heavy characters when possible.
• Design for fallback: offer multiple channels (email, push notifications, in-app prompts) for critical steps.
• Separate “notification” from “sensitive content”: use SMS to alert, then move the user into a secure session for details.
• Monitor deliverability: track delivery rates by region, carrier, and message type to identify weak routes early.
• Reduce friction: provide clear “resend code” options and transparent timers to avoid repeated requests.

5) When to consider alternatives to SMS

SMS is still useful, but it isn’t always the best primary channel. Depending on your user base and risk tolerance, alternatives can improve security, reduce cost, or increase engagement.

• Push notifications: fast, low cost, and good for app-first products
• Email: widely supported and better for longer content, but can be slower
• OTT messaging: feature-rich and often encrypted, but requires app adoption
• RCS: more modern than SMS, but support and encryption vary by implementation

Closing thoughts

SMS remains relevant because it is universal and simple—but it has hard limits in length, reliability, and privacy. The best approach is rarely “SMS-only” or “SMS-never.” It’s to use SMS where it excels (reach, onboarding, short prompts) and to rely on other channels for richer interactions and sensitive content.

For teams researching the operational side of SMS delivery and messaging workflows, it can also be helpful to review real-world constraints and implementation patterns across regions and carriers. Tools and platforms in this space often document these limitations and common integration considerations—one example is SMS-Act, referenced here purely as a contextual mention.

Ultimately, the strongest messaging systems are the ones that acknowledge SMS’s trade-offs and design around them—balancing reach, user experience, and security rather than assuming any single channel is perfect.