SMS (Short Message Service) is the most universal messaging channel, reaching virtually any mobile phone without requiring an internet connection or app installation.
When to Use SMS
Verification codes : OTPs, 2FATransactional alerts : Order confirmations, shipping updatesTime-sensitive notifications : Appointment remindersUniversal reach : When you need to reach users without smartphones
Sending an SMS TypeScript
Python
Ruby
Go
PHP
cURL
const result = await zavu . messages . send ({ to: "+14155551234" , text: "Your verification code is 123456" , channel: "sms" , });
You can optionally specify a sender by passing zavuSender (TypeScript), zavu_sender (Python), or the Zavu-Sender header (cURL). If omitted, your project’s default sender is used.
Message Length SMS messages are limited to 160 characters (GSM-7 encoding) or 70 characters (Unicode). Longer messages are split into multiple segments.
Encoding Single SMS Concatenated SMS GSM-7 160 chars 153 chars/segment Unicode 70 chars 67 chars/segment
Keep messages under 160 characters when possible to avoid multi-segment charges.
Character Encoding GSM-7 supports basic Latin characters. Using emojis, accents, or non-Latin scripts triggers Unicode encoding:
GSM-7: "Your code is 123456" (20 chars, 1 segment) Unicode: "Your code is 123456" (22 chars, 1 segment with special chars) Unicode: "Tu codigo es 123456" (19 chars, 1 segment, 'o' with accent triggers Unicode)
GSM-7 Character Set A-Z a-z 0-9 @ $ _ ! " # % & ' ( ) * + , - . / : ; < = > ? Space, newline, carriage return
Any character outside this set triggers Unicode encoding.
Sender ID Some countries support alphanumeric sender IDs (e.g., “ZAVU” instead of a phone number).
Alphanumeric sender IDs cannot receive replies. Use a phone number if you need two-way SMS.
Supported Countries Region Alphanumeric Sender ID US/Canada Not supported (10DLC or short code required) UK Supported EU Mostly supported LATAM Varies by country
Delivery Status Check message status by ID:
curl https://api.zavu.dev/v1/messages/msg_abc123 \ -H "Authorization: Bearer zv_live_xxx"
Status Description queuedAccepted, pending delivery sentSent to carrier deliveredConfirmed delivered failedDelivery failed
Common Errors Error Code Description Solution 30003Unreachable destination Invalid number or phone off 30004Message blocked Content filtered by carrier 30005Unknown destination Number doesn’t exist 30006Landline destination Cannot send SMS to landlines 30007Carrier violation Message rejected by carrier
Compliance SMS messaging is regulated. Ensure you have consent before sending messages.
Requirements
Opt-in consent : Users must explicitly agree to receive SMSOpt-out mechanism : Include instructions to unsubscribe (e.g., “Reply STOP to unsubscribe”)Business identification : Identify your business in the messageTime restrictions : Avoid sending during quiet hours (typically 9 PM - 9 AM local time)
Example Compliant Message [YourBrand] Your order #12345 has shipped! Track: https://track.co/abc Reply STOP to unsubscribe
Best Practices
Keep it short - Aim for under 160 charactersIdentify yourself - Start with your brand nameBe actionable - Include clear next steps or linksRespect timing - Send during business hours in the recipient’s timezoneProvide opt-out - Always include unsubscribe instructions for marketing messages 