SMS remains one of the most effective channels for business communication. It is widely supported, immediate, and direct. But using SMS for business also means following regulations that vary by country, choosing the right type of number, and understanding how messages are billed and delivered.
In this article, we will explain the key SMS concepts in detail — starting with the basics, then moving through sender types, capabilities, toll-free and 10DLC numbers, verification, and billing.
SMS basics
SMS (Short Message Service) is the foundation of business messaging.
Concept |
Explanation |
SMS |
Standard text messages. Works worldwide, up to 160 characters. Learn more about supported message types in this Help Center article. |
MMS |
Text messages with media (images, GIFs, videos). Learn more about supported message types in this Help Center article. |
Message segments |
Longer texts are split into multiple segments and reassembled on the recipient’s device. Each segment is billed separately. |
About message length:
- English and symbols → up to 160 characters = 1 SMS.
- Emojis or non-Latin languages (Chinese, Arabic, etc.) → only 70 characters fit into 1 SMS.
- Longer texts are split into pieces (“segments”). Each piece is billed separately.
Example: A long message with 300 Chinese characters = 5 SMS charges.
Sender types
Your sender type is the identity shown to customers when they receive your message.
Sender type |
What it is |
Best for |
Limitations |
US/Canada numbers starting with 800, 888, 877, etc. |
One consistent number across the US/Canada, brand trust, nationwide reach |
Works only in US/Canada, requires toll-free verification |
|
Local US 10-digit numbers with area codes |
Local presence, region-specific marketing, higher trust with local customers |
US only, requires brand and campaign registration |
|
Short codes |
5–6 digit numbers used for mass texting |
Campaigns, promotions, and alerts that need very high volume |
Not supported on SleekFlow |
Capabilities: What your number can do
Different number types support different messaging capabilities. Here’s how they compare:
Capability |
What it means |
Supported by |
SMS |
Standard text messages (up to 160 characters in English, or 70 characters with emojis/non-Latin scripts) |
All number types |
MMS |
Messages with images, GIFs, videos, or longer text |
Toll-free, 10DLC (US only) |
1-way communication |
You can send messages, but customers cannot reply |
Toll-free, 10DLC (US only) |
2-way communication |
Customers can reply to your messages |
Toll-free, 10DLC (US only) |
Toll-free numbers (US only)
Toll-free numbers give your business a nationwide presence with one consistent number.
Aspect |
What it means |
Definition |
Numbers starting with 800, 888, 877, etc., recognized across the US and Canada |
Best for |
Businesses that want a single trusted number for all customers across the country |
Capabilities |
Supports SMS and MMS, 2-way messaging, and higher sending speed after verification |
Verification |
Toll-free verification (TFV) is required before you can send messages |
Limitations |
Only works in the US and Canada, not available internationally |
10DLC numbers (US local numbers)
10DLC numbers are regular-looking phone numbers with local area codes, but approved for business messaging.
Aspect |
What it means |
Definition |
Local 10-digit numbers with area codes (e.g. 212 for New York) |
Best for |
Businesses that want a local presence and more trust with customers in specific regions |
Capabilities |
Supports SMS and MMS, 2-way messaging, and higher sending speed after registration |
Verification |
Brand and campaign registration required with US carriers |
Limitations |
Works only in the US, not suitable for international messaging |
Verification and compliance
To protect customers from spam, carriers require all businesses to verify their details before sending SMS.
Requirement |
What it means |
Business info (KYC) |
You must provide your company details before SMS is activated |
Toll-free verification (TFV) |
Required for all toll-free numbers in the US and Canada |
10DLC registration |
You must register your brand and campaign with US carriers |
Opt-in and opt-out |
Customers must give consent to receive SMS. They can reply STOP to unsubscribe or HELP for support |
Carrier filtering |
Unverified or non-compliant messages may be blocked by carriers |
Billing and delivery
Every SMS or MMS sent through SleekFlow is billed from your SMS wallet balance.
Concept |
What it means |
Wallet balance |
You need credits in your SMS wallet to send messages |
Per segment charging |
Messages longer than the limit are split into segments, and each segment is billed separately |
Monitoring |
You can track balance, usage, and delivery status in the SleekFlow dashboard |
Failed delivery |
Messages may fail due to low balance, invalid numbers, carrier blocking, or missing verification |
Learn more about managing SMS wallet in this Help Center article.