> ## Documentation Index
> Fetch the complete documentation index at: https://docs.arnio.co/llms.txt
> Use this file to discover all available pages before exploring further.

# SMS Campaigns - Concepts

> Learn key concepts for SMS campaigns.

# SMS Campaigns - Concepts

Learn key concepts for SMS campaigns.

## Message length

SMS messages are limited to 160 characters per segment. Messages longer than 160 characters are automatically split into multiple segments, which may incur additional costs.

## Character encoding

* **GSM-7**: Standard encoding, supports 160 characters per segment
* **UCS-2**: Unicode encoding, supports 70 characters per segment (for emojis and special characters)

## Delivery confirmation

SMS delivery reports help you track:

* Sent status
* Delivery confirmation
* Failed delivery reasons

## Opt-in requirements

Ensure you have proper opt-in consent before sending SMS campaigns. This is required by regulations like TCPA (US) and GDPR (EU).

## Short codes vs long codes

* **Short codes**: 5-6 digit numbers, best for high-volume campaigns
* **Long codes**: 10-digit phone numbers, more personal and flexible

**See also:**

* [SMS campaigns →](/campaigns/sms-campaigns)