Why SMS Sender Numbers Differ by Country
Every country has different rules for what a business SMS can use as a "From" address. Mobile networks worldwide set these rules to protect users from spam and scams.
The good news: TNZ handles this for you automatically and assigns the correct sender format based on the country you're messaging.
New Zealand Sender ID Rules
In New Zealand, all A2P Messaging (any SMS sent from a computer or application to a mobile phone) must use a Short Code. This is a 3-digit to 6-digit number authorised by New Zealand mobile network operators (Spark, One NZ and 2degrees) and monitored by the New Zealand Department of Internal Affairs.
- The Rule: You cannot send computer-based business SMS from a standard 021/022/027 mobile number. The mobile networks work with New Zealand's Department of Internal Affairs to block these messages and prevent spam.
- The Solution: TNZ assigns a Short Code to your account based on your message type (e.g. alerts, reminders, or marketing). You can start sending immediately. Many customers use a built-in shared Short Code successfully.
⚠️ You can't use your own mobile number!
NZ networks and the Department of Internal Affairs actively block business SMS sent from standard 021/022/027 numbers. This is to keep the channel trustworthy and prevent the kind of spam that other countries struggle with. TNZ provides a compliant Short Code on signup so you don't have to wait or apply for one yourself.
→ Wondering if one NZ number can do both SMS and voice? It can't. See Why You Can't Use One NZ Number for Both SMS and Voice for reasons and the recommended two-number setup.
Shared vs. Dedicated Short Codes
New Zealand businesses have two primary options for their Sender ID. Most TNZ customers use a built-in Short Code due to its cost-effectiveness and ease of use.
| Feature |
Built-In Short Code |
Dedicated 4-Digit Code |
Dedicated 6-Digit Code |
| Setup Time |
Instant |
4-6 Weeks |
4-6 Weeks |
| Setup Cost |
Free |
$600.00 |
$300.00 |
| Monthly Fee |
Included |
$299.00 |
$89.00 |
| Compliance |
Managed by TNZ |
Managed by TNZ |
Managed by TNZ |
| Best For |
Most businesses — reminders, alerts, notifications, 2FA |
High-volume marketing campaigns where maximum brand impact matters |
Cost-effective dedicated branding for medium-volume senders |
| Benefits |
- Lower cost
- Fast onboarding |
- Improved inbound SMS support
- Memorable number
- Option to absorb the inbound text cost (free for the mobile) |
- Improved inbound SMS support
- Lower fixed costs
- Option to absorb the inbound text cost (free for the mobile) |
You can upgrade to a dedicated one at any time from the dashboard (you don't have to commit upfront).
What happens to SMS replies after the 5-day reply window?
When you send an SMS, the recipient has a 5-day window to reply. Sending another message to the same mobile resets the timer. What happens after the window depends on the sender type:
| Sender type |
Reply received more than 5 days after the last outbound |
| Dedicated number (dedicated 4 or 6-digit Short Code, or AU Virtual Mobile Number) |
Routed to your account using the number's default inbound settings. You still receive the message, it's just no longer matched to a specific outbound thread. |
| Built-in Short Code |
The reply is dropped. Shared codes are pooled across customers, so an unmatched reply can't be safely attributed to anyone. |
⚠️ Keep conversations active on shared codesIf you need an ongoing two-way conversation on a built-in Short Code, send the next outbound message within 5 days of the previous one. Each outbound resets the reply window. For genuinely long-running conversations, use a dedicated number or the
SMS Reply Link, which captures replies via a web page and isn't subject to the 5-day window.
→ For a deeper walkthrough of NZ Short Codes (Standard Rate vs Free-to-Text and Spam Act compliance), see Understanding SMS Short Codes.
When should you consider a Dedicated Short Code?
A dedicated number is recommended if you are:
- Running SMS Marketing campaigns where strict Spam Act compliance is vital.
- Sending sensitive links that require network-level whitelisting.
- Building long-term brand recognition around a specific number.
- Allowing mobiles to initiate the conversation (the mobile sends the first message).
Australia Sender ID Rules
The Australian market operates under ACMA (Australian Communications and Media Authority) regulations, allowing for more flexibility in the "From" field:
- Virtual Mobile Number (Long Code): A full-length mobile number. This is the default for TNZ customers in Australia as it allows for two-way communication (capturing replies from Australian recipients).
- Alpha Sender ID: A brand name (up to 11 characters), such as "TNZ" or "YourBrand".
Note: Alpha tags must be pre-registered and approved by the Australian networks to comply with anti-scam legislation.
⚠️ Can NZ recipients reply to an AU Virtual Mobile Number?
Yes, Australian VMNs accept replies from any mobile number globally.
Keep in mind, TNZ cannot send to a New Zealand mobile from an Australian VMN - we must send using an NZ short code number.
→ See our Virtual Mobile Number and Alpha Sender ID guides.
Global Sender ID Rules
Each country sets its own rules for SMS Sender IDs.
TNZ will automatically handle setting the correct sender for you if the country's network operates allow it. If you message a specific country frequently, we can often provision a local number or register a localised Alpha tag to improve engagement and trust.
Some countries require additional compliance before you're allowed to send messages there. The SMS Geographies guide provides further detail.
Your Sender ID is typically configured during account onboarding by your TNZ representative. Settings can be applied at two levels:
- Per Account: One Sender ID applies to all users (e.g. all company messages come from the same code).
- Per User/Group: Unique IDs for different departments (e.g. Support uses one code, while Sales uses another).
If you need to check your current Sender configuration or "Copy" settings from an existing user to a new one, please contact our support team.