SMS remains one of the most reliable ways to reach customers instantly. It is widely used for alerts, notifications, reminders, and two-way support conversations. With SleekFlow, you can manage SMS messages alongside your other channels in one inbox.

In this article, we will guide you through what SMS is supported in SleekFlow, the available number types, and message limitations.

Benefits and use cases

Pain points solved:

• Direct customer reach: Deliver time-sensitive messages instantly to US customers.
• Unified inbox: Manage SMS alongside WhatsApp, Facebook, and other channels in SleekFlow.
• Compliance support: Use verified numbers to improve deliverability and reduce filtering.

Common use cases:

• Reminders: Appointment, billing, or event notifications.
• Alerts: Shipping updates, service outages, or urgent announcements.
• Two-way conversations: Customer support or order inquiries handled directly via SMS.
• Marketing and promotions: Deliver special offers, discount codes, or seasonal campaigns to boost engagement.

What’s supported in SleekFlow

SleekFlow currently supports SMS for the US market only. Two types of phone numbers are used for business messaging in the US: Toll-free numbers and 10DLC numbers.

Toll-free numbers

• What it is:
  • Toll-free numbers are nationwide numbers that start with a prefix like 800, 833, 844, 855, 866, 877, or 888. They are not tied to a specific location and are commonly recognized across the US.
• How it works in SMS:
  • Businesses can use Toll-free numbers to send and receive SMS and MMS messages with customers nationwide.
• Why it matters:
  • Gives your brand a professional, recognizable presence.
  • Customers won’t be charged extra for replying to your messages.
  • Carriers require a Toll-free Verification (TFV) process to approve your use case, which improves message deliverability and reduces the risk of filtering or blocking.
• Best for:
  • Companies that want one consistent number across the country — for example, customer support lines, nationwide campaigns, or service alerts.

10DLC numbers (coming soon)

• What it is: 
  • 10DLC stands for 10-Digit Long Code. These are standard US local phone numbers (e.g. a 212 number for New York). They look like a regular mobile or landline number, but are registered specifically for business messaging.
• How it works in SMS: 
  • Businesses use 10DLC to send SMS and MMS from a local area code, giving a more personal, “neighbor-like” impression.
• Why it matters:
  • Provides a local presence, which can feel more familiar and trustworthy to customers in that area.
  • Offers higher throughput (faster delivery and more messages per second) than unregistered long codes.
  • Requires 10DLC registration with US carriers, where you declare your business and messaging use case. This ensures compliance and prevents spam.
• Best for: 
  • Businesses that want to engage customers in a specific region, or that need multiple local numbers to support different markets.

Supported message types in SleekFlow SMS channel

SMS (Short Message Service)

Text

You can compose and send plain text messages directly.

• Character limits:
  • GSM-7 encoding (160 characters per segment): This is the standard character set used for most SMS. It includes basic Latin letters, numbers, and common symbols.
  • Unicode encoding (70 characters per segment): Used when your message contains special characters (e.g. emojis, Chinese, Arabic, accented letters). Because Unicode covers a wider range of characters, the per-segment limit is lower.

Messages longer than the limit are split into multiple segments (concatenated SMS)

MMS (Multimedia Messaging Service)

For the full list of supported message type, you can refer to the official documentation here

File names are highly recommended to follow these media file name guidelines:

• Don't use spaces.
• Keep file names to 20 characters or less.
• Avoid most special characters, such as ~ ! @ # $ % ^ & * ( ) [ ] { }.

Unsupported message types in SleekFlow SMS channel

The following are not supported when using SMS or MMS in SleekFlow:

• Files larger than 5 MB
• Unsupported file formats (e.g. .ZIP, .PSD, .EXE)
• Media files with invalid names (spaces, special characters, or missing extensions)
• High-risk or prohibited content as defined by Twilio and US carriers (e.g. sex, hate, alcohol, firearms, tobacco, cannabis/CBD)
• Emergency or 911-type traffic (not supported by Twilio numbers)