Whose number starts with 0423?
The 0423 mobile prefix appears in the ACMA register as held by OPTUS MOBILE PTY LIMITED, which holds every one of the window's 1m allocated numbers. The earliest allocation in 0423 is dated 10 July 2002 (to OPTUS NETWORKS PTY LIMITED, since transferred to OPTUS MOBILE PTY LIMITED).
Source: ACMA register, data as of 16/10/2026
The story of 0423
0423 is the odd one out among the Optus windows: the register names Optus Networks Pty Limited, the fixed-network company, as the original allocatee on 10 July 2002, with the transfer to Optus Mobile following on 10 February 2003 — eleven days after the rest of the Optus ranges were consolidated.
The 0423 ranges in the ACMA register
The 0423 window is covered by 1 allocation with a combined capacity of about 1m numbers, in the hands of 1 holder. The range has changed hands since allocation: the register still names OPTUS NETWORKS PTY LIMITED as original allocatee, with the transfer recorded on 10 February 2003.
| Range | Numbers | Original allocatee | Current holder | Allocated | Transferred |
|---|---|---|---|---|---|
| 0423000000–0423999999 | 1m | OPTUS NETWORKS PTY LIMITED | OPTUS MOBILE PTY LIMITED | 10/07/2002 | 10/02/2003 |
- 0423000000–0423999999 (1m numbers) was allocated on 10 July 2002 to OPTUS NETWORKS PTY LIMITED and transferred on 10 February 2003 to OPTUS MOBILE PTY LIMITED.
Optus Mobile in 0423 and nationally
OPTUS MOBILE PTY LIMITED holds 1m numbers in 0423 — the whole window — which is a small slice of its 29.4m mobile numbers nationally, or about 34% of every allocated Australian mobile number. The register places Optus Mobile in 24 different 04xx prefixes, including 2 of the other nine in the 0420–0429 decade (0421, 0422).
| Holder | Numbers in 0423 | Share of 0423 | Share of all 04 numbers | Prefixes held |
|---|---|---|---|---|
| OPTUS MOBILE PTY LIMITED | 1m | 100% | 34% | 24 |
The other prefixes in the 0420–0429 decade
Held by Vodafone Australia, Optus Mobile and Telstra: 0420, 0421, 0422, 0424, 0425, 0426, 0427, 0428, 0429. The decade's oldest allocation is in 0429 (18 September 1998, Telstra), its youngest in 0426 (28 May 2010, Vodafone Australia). One prefix in the decade is split between several holders: 0420.
What does a call from a 0423 number mean?
Standard mobile rates. The Optus Networks allocation is a corporate detail, not a hint about the caller: 0423 numbers are ordinary consumer and business mobiles.
No published reports for this prefix yet.
Had a call from a 0423 number?
No clear pattern in reports on these numbers yet. If a call worried you:
- Call back on a number you trust
If a caller says they're your bank, the ATO, Services Australia, a courier or your telco, hang up and ring the organisation on the number from its website or your statement, never the number that called you. Caller ID can be faked.
- Report the call to Scamwatch
The National Anti-Scam Centre uses Scamwatch reports to warn others and to get scam numbers blocked. Note the number, the time and what the caller claimed to be. If anyone is in danger, call 000.
- Register on the Do Not Call Register
Registering landlines and mobiles is free and stops most telemarketing calls within 30 days. Charities, political parties, surveys and scammers aren't covered.
- Forward spam texts to 0429 999 888
The ACMA collects unsolicited commercial texts forwarded to 0429 999 888 (standard message charges apply). Don't edit the message first. Scam texts that impersonate a bank, toll road or delivery company go to Scamwatch instead.
Nationally, Scamwatch recorded $72.5 million lost to scams that started with a phone call in 2025 (down from $107.2 million), with a median loss of $3,800 per report that lost money, and phone-call scam reports are 73.7% below their 2021 level. Telcos blocked 109.3 million scam calls and 45.2 million scam texts in January to March 2026. Sources: Targeting scams 2025 (National Anti-Scam Centre); ACMA quarterly report, Jan–Mar 2026.
0423 numbers: questions and answers
Which network does a 0423 number belong to?
The ACMA register lists Optus Mobile as the holder of every allocated number in 0423 (1m numbers). Mobile numbers can be moved to another network, so the caller may now be with a different provider.
When was 0423 first allocated?
The earliest 0423 range in the register is dated 10 July 2002, to Optus Networks. The window is covered by 1 register range.
How big is Optus Mobile's share of Australian mobile numbers?
Across the whole 04 range, Optus Mobile holds about 34% of allocated mobile numbers, spread over 24 of the 04xx prefixes.
How do I report a scam call or text from a 0423 number?
Report scam calls and texts to Scamwatch. Forward unsolicited commercial texts to the ACMA on 0429 999 888, and block the number from your phone's recent calls or messages. If you lost money, call your bank first, then report it through ReportCyber.
Check a 0423 number
Range data is not personal data and the number on your screen can be spoofed. Scam calls: Scamwatch. Guides: Who called me from this number?, Which carrier owns which mobile prefix?